Natural Resources Wales and Environment Agency plan to eradicate the invasive non-native Topmouth gudgeon from a popular lake in Llanelli.

In early January 2023, the two agencies will start work to remove the fish from Sandy Water Park to protect the future of the lake, as well as waterways throughout Wales and England. The work has been funded by Welsh Government and is supported by landowners, Carmarthenshire County council.

Topmouth gudgeon are native to Asia, but have spread rapidly throughout Europe. The invasive fish poses a significant threat to the ecology and wildlife of rivers and lakes, and the fisheries that they support.

The silver-coloured fish eat eggs and larvae of native fish and reproduce rapidly, spawning up to four times a year. This behaviour can significantly reduce stocks of native fish by outcompeting them for food an habitat. They can also spread disease and parasites that pose a threat to our native species.

Sandy Water Park is one of 34 known sites across England and Wales where the invasive fish have been found. Work will begin to eradicate Topmouth gudgeon in the first week of January 2023 and will take approximately four weeks to complete.

Naturally occurring chemical specifically designed to kill fish will be applied

Water in the lake will be reduced and larger, healthy fish including carp and tench, will be removed and relocated.

A piscicide containing rotenone, will then be applied to the water to kill the Topmouth gudgeon population. This is a naturally occurring chemical like a pesticide or herbicide specifically designed to kill fish.

Rotenone is the most effective and humane way to remove Topmouth gudgeon, causing them minimum distress. Mammals, birds and shellfish are highly resistant to the chemical and are not affected. It will also not present any risk to park users. Public access around the lake will be restricted while the work is being carried out.

Rotenone naturally breaks down in the water, which NRW will be monitoring continuously until it is no longer present, after which the lake can be restored to their former, natural state.

For further information see the NRW website here.