Fish are to be moved from a small river near the site of the proposed Olympic stadium in east London.
Fish will be moved to the River Lea
The water of Pudding Mill River in Stratford will be gently electrified to stun the fish and make them float to the surface, aquatic experts said.
Species such as eel, tench, bream and pike, will then be carefully retrieved and released into the nearby River Lea.
The work marks the start of the Olympic authority's project to protect wildlife living on the building site.
Experts said Pudding Mill River was not a healthy spawning ground but did host several species.
Traps will also be laid to round up newts.