A task force set up by Natural Resources Wales (NRW) to tackle illegal modifications to rivers has seen more than 30 legal notices served to landowners.
Wales has experienced an 'unprecedented increase' in unconsented physical modifications to its watercourses, the environmental watchdog said.
These include actions such as dredging, removing shoals, realignment of water courses and inappropriate bank protection.
The NRW said these types of modification caused "long-term damage, potentially lasting many decades".
A task force was established to respond to such incidents, with the NRW delivering 30 regulatory notices on unconsented work since.
Regulatory notices are legal documents that can be issued to a landowner or contractor to stop unconsented work and to restore it.
Oliver Lowe, specialist advisor for NRW said: “Our improved response is changing landowner behaviours as word of our action spreads.
"We also have the option of pursuing prosecution if the incident is particularly severe. Should a notice not be complied with then this can result in a fine and criminal prosecution.”
In 2021, works were undertaken on a river to install a gabion basket wall which resulted in the narrowing of the channel, which increased water velocity and erosion.
NRW officers visited the site to stop the work and then issued a formal notice to the landowner to restore the river channel.
Since then, the landowner has restored the bank profile, reseeded the ground with native wetland grasses and wildflowers are being planted on the bank to improve stability.
Hilary Foster, another advisor who works for NRW, said the 'improved response' to these incidents was 'successfully protecting our rivers from harm'.
"This work has generated interest from the regulatory authorities in England, Scotland and as far afield in Norway.
“If you are considering undertaking any work on a watercourse you should contact NRW for advice. We will provide information on any necessary permissions and measures to avoid environmental harm."
It comes after a Herefordshire landowner was recently ordered by Natural England to restore a section of the River Teme which he cleared without permission.
