There are many different habitats within the tidal waters of the Helford, from rich rocky shores and reefs to sandbars and mud, which in turn supply homes to a wealth of wildlife.
The exposed rocky shores and submerged reefs at the mouth of the estuary are home to a colourful array of sea anemones, star-fish, sea urchins, sponges, sea squirts, lobsters and crabs, whilst offshore there are small beds of maerl, a rare slow-growing calcified seaweed.
The sands and mud in the more sheltered water upstream support vast numbers of invertebrates, including the peacock worm (Sabella pavonina) which can be seen in shallow water spreading its fan-like tentacles to catch food.
Eelgrass is the only British flowering plant to be found growing in the sea. Tufts of green leaves arising from underground stems provide important shelter for crabs, anemones and young fish whilst cuttlefish, sea hares and sea lemons use it to anchor their eggs. Perhaps one day the fascinating little sea horse will be seen again within the underwater meadows. Recently concern has arisen that boat anchors are contributing to bare patches, so attempts are being made to persuade boat owners to anchor elsewhere in the estuary.
No less than 800 species of fish have been recorded in the Helford waters which are an important feeding and nursery area for many species with bass being of particular interest.
The Helford provides winter feeding grounds for a variety of waders and gulls on the adjacent fields and mudflats, while a selection of divers, grebes and ducks can be found in the deeper water near the mouth. Migrant ospreys can be seen each year. Residents include herons, little egrets, kingfishers, shelduck, fulmars and ravens.
Common cord-grass (Spartina sp) fringes many of the upper Helford creeks forming dense beds where the roots entrap mud and, as the tides rise and fall, offer rich feeding opportunities to birds such as heron and many fish such as juvenile bass and mullet living in the warm waters.
Although the woods fringing much of the estuary still contain part of the original ancient Oak Woodland, such as at Merthen, some of them are dominated by introduced species. However the woods support abundant wildlife and the mild humid climate is ideal for ferns and mosses.