The Fleet lagoon is an area of water between Chesil Beach and the mainland. It is 13.1 km (8.2 miles) long and covers an area of approximately 480 hectares. The width varies from 900 metres at Littlesea down to just 65 metres at The Narrows.

The bed of the Fleet is mostly mud and broken shell with some gravel patches.The water is deepest in the lower Fleet where it is up to 4-5 metres deep. Most of the upper Fleet above The Narrows is no more than 2 metres deep. The Fleet connects to the sea at Ferrybridge and then out through Portland Harbour. Sea water can also enter the Fleet from Lyme Bay during storms and by percolation through the beach at certain states of the tide. Fresh water enters the Fleet by rainfall and from a number of streams that feed into the Fleet. At Ferrybridge the water is normal seawater with a salinity around 35 parts per thousand (ppt) but at Abbotsbury the salinity can fall below 16ppt.

The water in the Fleet is generally warmer than the surrounding sea in the Summer but colder in the Winter. In the lower Fleet the water temperature can vary by more than 4°C due to the interaction with the exposed sand banks.

The Fleet is an important area for wildlife and has received a number of designations:

Special Area of Conservation (SAC)

Special Protection Area (SPA)

A RAMSAR site

A Site of Special Scientific Interest (SSSI)

Designated bass nursery area

Visit the Designations page for more information. In the mid-Fleet there are extensive beds of eel grass (Zostera) and tasselweed (Ruppia). In the lower Fleet there is a wide range of marine algae.Some Summers the invasive species Japanese seaweed, Sargassum muticum, can be widespread.

The Fleet derives its name from the Saxon 'fleot', meaning shallow water

The bed of The Fleet has been owned by the Ilchester Estates since 1539

The lower Fleet looking northwards towards the Narrows

The mid-Fleet looking southwards towards the Narrows and Portland.

Over 150 species of algae (seaweed), 25 species of fish and 60 species of molluscs have been found in the Fleet

Mid and upper Fleet looking from Abbotsbury Hill towards the Narrows with Portland in the distance