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Removing barriers to fish migration on the Odney

The Odney stream is one of the most valuable spawning grounds on the Thames for flow dependent fish species such as chub and dace. However, in recent years, the stream has been affected by low summer flows, caused by a weir at the head of the channel.

It was crucial for us to address this situation, so we've recently completed a £10,000 project in an attempt to overcome the barriers to fish migration on the stream. Rock ramp will improve fish passage

The project involved modifying the existing weir by cutting a two-stage, 400mm notch along its length. The channel bed was also raised to ‘drown-out’ the weir and 40 tonnes of large rocks and gravel were placed into the channel so that the weir would still be passable for fish. Each rock was placed very carefully to leave enough room for fish to swim between them.

“As well as maintaining flows, the modifications means fish can now pass the weir easily,” explains fisheries officer, George Gerring. “The new gravel will also provide additional spawning habitat for fish along a 100-metre section of the stream.”

We are confident these improvements will make a big difference to the numbers of fish now able to reach valuable spawning areas on the Odney – and we will be monitoring the situation very closely this summer.