Viable fish stocks have returned to the waterways, with some 400 salmon taken from the Kelvin last year alone.
As a result, efforts to govern activity in the river have intensified, with Marine Scotland upping the number of permits issued to water bailiffs, who have powers of arrest and seizure.
The number of bailiffs patrolling the Kelvin – which flows through the West End to join the River Clyde – has doubled in the past two years to more than 30 in an attempt to combat illegal fishing.
Water bailiff Paul Reid, secretary of the River Kelvin Angling Association, said: "Given the recovering salmon and trout population, we are now at a stage where we are seeing fairly standard poaching methods being used on the river.
"In the past, there was no point in poachers coming to the Kelvin, but that is no longer the case.
"The increased numbers in salmon and trout means we are having to do more to police the river and also educate people about what is permitted."
Strict rules govern legitimate fishing on the Kelvin, which is leased from the Crown Estate and managed by the River Clyde Fisheries Management Trust, with around 70% of all fish caught returned to the river.
However, Mr Reid, 34, said there had been recent evidence nets had been placed in the river, as well as multiple hooks running on lines tethered to the river bank to catch the fish indiscriminately.
Mr Reid added: "There are professional organisations that travel the length and breadth of Scotland to basically stake out a river and are likely to work late at night netting part of a river.
"You also have the fun angler who wants to fish the local river when the sun comes out.
"The third group, and the last group, are the chancers, the people who know you require a permit but who think nobody will bother."
Water bailiffs have powers to arrest, seize tackle and confiscate vehicles used in the poaching operation.
A report will then be made to the procurator fiscal when necessary.
