A rare French worm and an endangered hairy German snail have been found in an east London river.
About 200 German hairy snails per square metre were discovered
Ecologists made the find after examining 20 sites along the River Lee, in east London, and Bow Back Rivers.
The sites have been earmarked for an 80,000-seat Olympic stadium, arenas, and a water sports centre.
The ecologists were conducting a study to assess the potential impact of development along the lower reaches of the River Lee.
Almost 2,000 small worms, also known as the oligochaeta annelid, were discovered in the Walthamstow Marshes and Springfield Marina.
They are usually only found in limited parts of France, Belgium and Holland and have never been recorded in the UK before.
Two million snails
Groups of endangered German hairy snails, or perforatella rubiginosa, were also found in reed beds on the Channelsea River in West Ham.
There are thought to be about two million of the snails, which measure just 5mm across, in the area.
Environment Agency officer Karen Gowlett said: "This survey has highlighted the ecological value of the lower reaches of the Lee, which contain many habitats and species that are important both locally and nationally.
"The information will help the Environment Agency provide advice to help preserve and protect this special area."
Although neither species are legally protected under the Wildlife and Countryside Act, the agency said local authorities must consider any impact on such species when ruling on planning applications.