Melbourne's temperate waters offer year-round diving, but the experience changes dramatically from month to month. Water temperatures swing by more than 10 degrees across the year, visibility shifts with the seasons, and different marine species take centre stage at different times. Whether you are planning your first dive in Port Phillip Bay or trying to decide when to take annual leave for a week of diving, this month-by-month guide covers everything you need to know about what to expect underwater in Melbourne throughout the year.
One constant: Melbourne's weather is notoriously unpredictable. A forecast for a calm, sunny day can change within hours. The best approach is to stay flexible, check conditions on the morning of your dive, and have a backup site in mind. Use the Shore Dives condition scores to see real-time scoring for over 130 dive sites based on current wind, swell, and tide data.
Year-Round Residents
Before diving into the seasonal calendar, it is worth noting that several of Melbourne's most popular marine species can be found at any time of year. Nudibranchs carpet the pylons and reef at pier sites in every season, with dozens of species present across Port Phillip Bay and Western Port. Seahorses — both the short-headed seahorse and the pot-bellied seahorse — cling to seagrass and sponge gardens year-round, though they are easier to spot in winter when seagrass thins. Octopus are reliably found at almost every rocky site, and various ray species patrol sandy bottoms in all months. These year-round residents mean that no matter when you dive Melbourne, there is always something to see.
Summer: December, January, February
Summer is peak diving season in Melbourne. Long days, warm surface temperatures, and generally calmer conditions make this the most comfortable time to be in the water. It is also when Melbourne's underwater world is at its most vibrant and active.
December
Water temperatures climb through December, typically ranging from 15°C to 18°C. Visibility is often excellent, regularly reaching 8 to 12 metres at bay sites and even further at ocean-facing sites on the Mornington Peninsula. The warming water triggers increased activity across the reef, and fish life is abundant.
December is prime time for weedy seadragons carrying eggs. Male seadragons brood eggs on the underside of their tails from late spring through early summer, and December offers some of the best opportunities to observe males with bright pink egg clusters. Flinders Pier, Portsea Pier, and Rye Pier are all reliable locations. Fur seals become increasingly active and playful at sites near the Heads, making boat dives to Pope's Eye and the Chinaman's Hat area particularly rewarding — see our seal encounters guide for the best sites and interaction tips.
What to wear: A 5mm wetsuit is comfortable for most divers, though those who feel the cold may prefer a 7mm. Hood and gloves are optional but recommended for longer dives.
January
January typically delivers the warmest water temperatures of the year, with readings of 17°C to 21°C in sheltered bay sites. Surface temperatures in shallow areas can occasionally reach 22°C during sustained heatwaves. Visibility remains good, averaging 6 to 10 metres, though algal blooms triggered by warm temperatures can occasionally reduce clarity to 3 to 5 metres at some locations.
Marine life is at peak activity. Schools of fish are dense around pier pylons, and predators including Australian salmon and kingfish hunt through the shallows. Weedy seadragon eggs begin hatching in January, and patient divers may witness tiny juvenile dragons emerging. Blue-ringed octopus are more frequently spotted during the warmer months — beautiful but a reminder to look and never touch. Fur seals at the bay entrance are at their most playful, often approaching divers for extended interactions.
What to wear: A 5mm wetsuit is standard. Some divers are comfortable in a 3mm on the warmest days. Minimal thermal accessories needed.
February
February continues the warm water trend, with temperatures holding between 17°C and 21°C. Water clarity can be variable — afternoon sea breezes that build through summer create chop and can reduce visibility at exposed sites. Morning dives, particularly on weekdays, typically offer the best conditions and the clearest water.
This is an excellent month for diving the bay's more exposed sites. The Heads area, including rock walls and drift dives, benefits from warm water and good visibility. Bandicoot fish and old wives are abundant at pier sites, and stingarees and smooth rays are regularly encountered on sandy patches. Late February also marks the beginning of the transition toward autumn, with some species starting to shift their behaviour as water temperatures plateau.
What to wear: A 5mm wetsuit remains the standard. Consider a lightweight hood for dives beyond 45 minutes, as even warm water draws heat over extended bottom times.
Autumn: March, April, May
Autumn is arguably the best overall season for diving in Melbourne. Water temperatures remain comfortable, summer crowds thin out, and several of Melbourne's most spectacular marine events occur during these months. Experienced local divers often cite March through May as their favourite time of year to be underwater.
March
Water temperatures remain warm, sitting between 17°C and 20°C. The sea breeze pattern that defines Melbourne's summer begins to weaken in March, and many days deliver light winds and excellent surface conditions. Visibility is frequently outstanding, reaching 10 to 15 metres at ocean-exposed sites.
Fish life remains prolific from the summer peak. Schools of old wives shimmer around pier pylons, and ornate cowfish cruise the reef. March is a transitional month — the summer species are still active while autumn arrivals begin appearing. It is an excellent time for photography, combining warm water comfort with improving visibility.
What to wear: A 5mm wetsuit is still comfortable for most. Longer dives may warrant stepping up to 7mm, particularly in deeper water where thermoclines can drop temperatures by several degrees.
April
Temperatures begin their descent, ranging from 15°C to 18°C. Autumn weather patterns bring more variable conditions — calm, clear days interspersed with frontal systems passing through. The key to good April diving is watching the weather windows and being ready to dive when conditions align.
Giant Australian Cuttlefish begin appearing at pier sites in April. While numbers build through the coming months, early sightings at Flinders Pier and Portsea Pier are always exciting. The cuttlefish move into shallower waters as temperatures drop, setting the stage for the spectacular winter breeding season. Leafy seadragons — rarer than their weedy cousins — are occasionally spotted at deeper reef sites along the peninsula.
What to wear: A 7mm wetsuit becomes the standard choice. Hood and gloves are recommended, particularly for second dives when your body has already lost heat.
May
Water temperatures drop to 13°C to 16°C, and autumn is firmly established. Visibility can be exceptional in May — the reduced algal growth and less plankton in cooler water produce some of the clearest conditions of the year. Days of 10 to 15 metres visibility are not uncommon at pier sites, and boat dive sites can exceed 20 metres.
May and June mark the beginning of the extraordinary spider crab aggregation. Thousands of spider crabs gather in shallow waters, particularly in the southern reaches of Port Phillip Bay, to moult their shells in enormous piles. Blairgowrie and Rye are key sites for witnessing this event, which covers the seafloor in a living carpet of crabs. Giant cuttlefish numbers continue building at pier sites, and encounters become increasingly frequent.
What to wear: A 7mm wetsuit with hood, gloves, and boots is the minimum. Drysuit divers begin to appreciate their investment as bottom times extend. Cold-water diving is about comfort — being properly insulated lets you slow down and observe behaviour rather than rushing through a dive.
Winter: June, July, August
Winter diving in Melbourne is not for the faint-hearted, but it rewards those who brave the cold with unique marine encounters, outstanding visibility, and the quiet satisfaction of having the underwater world largely to yourself. Crowds disappear, and the divers who remain tend to be experienced and passionate about Melbourne's temperate marine life.
June
Water temperatures settle into their winter range of 11°C to 14°C. Wind patterns shift to predominantly northerly and westerly, which means many bay sites on the eastern side of Port Phillip are well-sheltered. When the weather cooperates, June delivers some of the year's best visibility — 10 to 15 metres at pier sites is achievable on calm days.
The spider crab aggregation typically peaks in June, with staggering concentrations of crabs piling on top of each other as they moult. This is one of Melbourne's most unique natural spectacles, and divers travel from across Australia to witness it. Giant cuttlefish are now in full breeding mode at sites including Flinders Pier, Portsea Pier, and Blairgowrie. Courtship displays — males flashing vivid colour patterns and competing for females — are mesmerising to watch.
What to wear: A drysuit is strongly recommended for comfortable winter diving. If diving wet, a 7mm semi-dry with hood, thick gloves, and boots is the minimum. Hand warmers in your car for after the dive are not a luxury — they are a necessity.
July
The coldest month for water temperatures, with readings of 10°C to 13°C. Air temperatures are also at their lowest, making surface intervals chilly and pre-dive preparation a test of motivation. However, those who push through are rewarded. Visibility on calm winter days is frequently the best of the entire year, and marine life encounters are intimate and unhurried with no competition from crowds.
Port Jackson sharks arrive at Flinders Pier in July and August, resting under ledges and in crevices along the pier pylons. These docile, distinctively patterned sharks are a highlight of the Melbourne diving calendar and can be observed at very close range. Giant cuttlefish breeding activity continues at its peak, and egg-laying behaviour is commonly seen. The combination of Port Jackson sharks and breeding cuttlefish makes Flinders Pier arguably Victoria's most compelling dive site during July.
What to wear: Drysuit territory without question. Even the most cold-tolerant wetsuit divers are reaching for their drysuits in July. Thermal undergarments, dry gloves if your system supports them, and a thick hood are essential. Plan your dives to be shorter and more focused — quality over quantity.
August
Water temperatures begin a slow climb, sitting between 10°C and 13°C. August often delivers stable weather patterns after the mid-winter lows, and there can be stretches of calm, clear days ideal for diving. The water remains cold but feels less punishing than July's lows.
Port Jackson sharks remain at Flinders Pier through August. Giant cuttlefish breeding activity starts to taper off as the season draws toward its end, though individuals can still be found at most pier sites. August is also a good month for exploring deeper reef sites along the peninsula where visibility tends to be excellent and the marine life, including large sponge gardens and gorgonian fan corals, is best appreciated in the clear winter water.
What to wear: Drysuit remains the recommendation. Conditions are similar to July, though the gradual warming trend offers a psychological boost. By late August, the most cold-sensitive divers begin contemplating the transition back to thick wetsuits.
Spring: September, October, November
Spring is a season of renewal underwater. Temperatures climb, marine life becomes increasingly active, and the diving community emerges from its winter hibernation. Spring conditions can be variable — Melbourne's spring weather is famously unpredictable — but the good days are truly excellent.
September
Water temperatures begin their upward trend, ranging from 11°C to 14°C. Conditions remain winter-like through much of September, with northerly winds and occasional storms. However, the increasing daylight hours trigger changes in the marine environment. Algae begins growing on reef surfaces, seagrass meadows start to thicken, and fish activity noticeably increases.
September offers an overlap of winter and spring species. Late-season cuttlefish may still be encountered at pier sites, while spring arrivals begin appearing. Southern right whales and humpback whales migrate along Victoria's coast during September and October — while unlikely to be seen on a shore dive, boat divers occasionally have extraordinary encounters. Nudibranchs are at their most diverse in spring, with species emerging to feed on the fresh algal growth.
What to wear: A 7mm wetsuit with full accessories is the minimum, and many divers continue using their drysuits through September. The water is still genuinely cold, and spring air temperatures are deceptive — a sunny day does not mean warm water.
October
Temperatures climb to 13°C to 16°C, and the underwater world begins to transform. Visibility can be mixed in October — spring plankton blooms occasionally reduce clarity, but between blooms the water can be wonderfully clear. Wind patterns become more variable, with the first sea breezes of the season beginning to appear on warmer days.
Marine life is noticeably more active than in winter. Seahorses become easier to spot as they move into mating behaviour, with males developing their brood pouches. Male weedy seadragons begin courting females, and by late October the first egg transfers from female to male may occur — the start of the breeding cycle that will produce December's egg-carrying males. Octopus are particularly active in spring, hunting aggressively as temperatures rise.
What to wear: A 7mm wetsuit suits most divers. Drysuit users can begin to consider switching to wetsuits for comfort and ease, depending on personal cold tolerance. Hood and gloves are still advisable.
November
Water temperatures reach 14°C to 17°C, approaching summer comfort levels. Visibility is generally good, though spring plankton activity can still cause variability from day to day and site to site. Afternoon sea breezes become more frequent, so morning dives are often the better choice.
November is when the diving season truly kicks into gear for the broader community. Dive clubs run more frequent trips, boat charters increase their schedules, and the pier sites see more activity. Underwater, the transition to summer is well underway. Weedy seadragons are in full courtship and egg-transfer mode. Fur seals at the Heads begin displaying the boisterous behaviour that makes summer seal dives so popular. Fish species that retreated to deeper water during winter return to the shallows in numbers.
What to wear: A 5mm to 7mm wetsuit depending on personal preference and planned bottom time. Lighter thermal accessories become feasible. November is the sweet spot where the water is warm enough for comfort but cool enough that you are not overheating on the surface in a thick suit.
Planning Around Melbourne's Weather
No seasonal calendar can fully account for Melbourne's capacity for weather surprises. A calm July day can deliver better diving conditions than a windy January day. The most successful Melbourne divers share a few habits worth adopting:
- Check conditions on the day, not just the forecast. Wind and swell can change rapidly. Use the Shore Dives scoring tool for real-time condition assessments across all Melbourne dive sites.
- Have a backup site. If your planned site is blown out, a different part of the bay may be sheltered. Pier sites in Port Phillip Bay offer protection from different wind directions — learn which sites suit which conditions.
- Dive mornings when possible. Morning conditions are almost always calmer than afternoons, particularly in the warmer months when sea breezes build through the day.
- Watch for weather windows in winter. High-pressure systems in winter bring light winds, clear skies, and outstanding visibility. These windows may only last a day or two, so be ready to take advantage when they appear.
- Respect your limits. Cold, low-visibility, or rough conditions increase risk. If conditions do not feel right, calling the dive is always the correct decision. Melbourne has over 130 shore dive sites — there will always be another opportunity.
Month-by-Month Summary
To help with quick planning, here is a condensed overview of the diving year:
- December: 15-18°C, excellent visibility, seadragon eggs, active seals
- January: 17-21°C, warmest water, peak marine activity, great for beginners
- February: 17-21°C, warm but watch for afternoon chop, good all-round diving
- March: 17-20°C, improving visibility, thinning crowds, outstanding conditions
- April: 15-18°C, cuttlefish arriving, variable weather, stepping up thermal protection
- May: 13-16°C, spider crabs beginning, crystal visibility, cuttlefish building
- June: 11-14°C, spider crab peak, cuttlefish breeding, drysuit season
- July: 10-13°C, coldest water, Port Jackson sharks, best visibility of the year
- August: 10-13°C, sharks continuing, stable conditions, excellent deep-reef diving
- September: 11-14°C, spring awakening, whale season, nudibranch diversity peaks
- October: 13-16°C, marine life ramping up, seadragon courtship begins
- November: 14-17°C, diving season kicks off, seals returning, warm-up continues
Melbourne's temperate waters may not have the tropical warmth of the Great Barrier Reef, but what they lack in temperature they more than compensate for in diversity and character. Every month brings something different, and the rhythm of the seasons gives Melbourne diving a depth and variety that keeps local divers coming back year after year. Check the Shore Dives page to find the best conditions for your next dive, whenever you decide to get in the water.