Mornington Pier, first built in the 1850s and rebuilt with a stone breakwater in recent years, is the busiest dive site on the northern half of the Peninsula and one of the most varied of the bay's pier dives. It runs about 200 m to the north-east from Schnapper Point, the rocky headland that shelters Mornington Harbour, and the depth range of 1–12 m is unusual for a Port Phillip pier: the inner section is seagrass, boulders and ledges in a few metres, the middle is silty sand with pylons thick with sponge and ascidian growth, and the head drops onto a soft mud bottom where the bigger rays and the occasional large snapper appear. West of the pier, the edge of Schnapper Point is a reef of tumbled rock and seagrass-covered boulders that many divers treat as a separate dive (The Scuba Doctor lists it as Schnapper Point, 2–10 m); it is the best part of the site for cuttlefish, octopus and old wives.

The pylons carry the standard Peninsula pier cast – big-belly and short-head seahorses, globefish, decorator crabs, moonlighters, dusky morwong, squid hanging in the shadows – with shrimp and nudibranchs in the growth and gurnards and whiting on the sand. Giant Australian cuttlefish are reliable in winter and spring, and spider crabs pass through in late autumn. The dive is run as a loop: out along one side, back along the other or via the point reef.

Its main disadvantage is the entry, a 3 m giant stride off the harbour wall and a climb back up long ladders, which is hard work with heavy gear and unsuitable when a westerly swell is running. Against that, it has free parking at the water's edge, a café and toilets on the pier, and consistently more fish than the flatter piers to the north. It suits Open Water divers, training groups, night divers and photographers, and it is the default fallback for the whole Peninsula when a southerly is blowing.

From Mornington Main Street drive down to Schnapper Point Drive and follow it to the pier car park at the end, which is free and usually has space right at the dive entry; if it is full, park along Schnapper Point Drive and walk 200 m or more. The classic entry is a giant stride off the 3 m high car-park wall beside the fixed ladders on the western side of the pier root; the alternative is to lower gear onto the stone ledge in the small boat inlet and step in from there. Exit by climbing the high ladders or by hauling out onto the stone ledge and passing gear up to the wall.

Avoid the eastern side where boats moor.

Mornington Pier is best with light-to-moderate south-westerly through easterly winds and a high tide, and is one of the few Peninsula piers that stays diveable when the southern bay and the ocean are blown out by southerlies. Its weakness is the north and west: strong northerly winds and any westerly swell coming down the bay wrap around Schnapper Point and make the entry wall and the ladders hazardous, and visibility drops sharply. Avoid it in northerlies above about 15 knots.

Boat traffic in and out of the harbour is constant in summer, so surface swims should be short and flagged. Night dives are excellent on calm evenings.

Stride in beside the ladders, descend to 3–4 m and follow the pylons out along the western side to the pier head, where the bottom reaches 10–12 m of silt and seagrass rock. Turn at the head, cross under the pier and come back on the western reef along the edge of Schnapper Point in 4–8 m, finishing among the boulders and seagrass at 3 m below the ladders for a natural safety stop.

A regular training and guided-dive site for Aquability and Diveline (Frankston) and Peninsula dive clubs; The Scuba Doctor runs guided shore dives here on request. No boat needed; most divers come independently.