A fish trap found in a Fen drain has been handed over to the Environment Agency, which is now investigating.
The 30ft fyke net was found by PAC members in the Sixteen Foot near March, Cambs, on Saturday.
After releasing the 50 or so eels and other coarse fish it contained, they removed it from the river.
Angling Times, which launched a high-profile campaign against fish theft earlier this year, has photographed the find and is now making its own enquiries on the story.
Two weeks ago, the EA's head of fisheries told the paper fish stealing from Britain's waterways was not a problem.
The PAC has been in talks this week with a third major bait supplier over adopting the club's Pikemark.
Firms can use the logo to assure customers that their baits come from legal and sustainable sources.
The club is calling on all anglers to remain vigilant and use the EA's hotline number to report suspicious activities 0800 807060.