The River Tawe is getting a spring clean thanks to a revolutionary system designed and built in Wales.
The water quality in the lower reaches of the river plummetted after the Swansea Bay Barrage was impounded in 1992.
Now bubble power is bringing the river up to the standards demanded by the Environment Agency.
The problems experienced on the Tawe after the barrage was built can happen wherever there is a man-made barrier between the sea and the river.
At high tide, seawater comes over the top of the barrage and is not allowed back out.
Lack of oxygen
Because it is heavier than fresh water, it sits on the bottom of the river, depriving freshwater fish of much-needed oxygen.
The system pumps columns of bubbles up from the river bed, mixing the salt and fresh water and simulating the process of ebb and flow which would happen naturally if the barrage was not there.
The system was designed by Swansea Council and the Mold-based Environmental Advice Centre.
They are hoping that the technique will be used to solve the same problem elsewhere, possibly at the recently-impounded Cardiff Bay Barrage.