More than 30 bags filled with cannabis were found by members of the Whittlesey Angling Club last month - and yesterday a second haul of the drugs was found.
Police are now investigating the finds.
Volunteer bailiff Roy Bridson was called on February 27 to the first find.
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Roy, a member of the Angling Trust’s Voluntary Bailiff Service, alerted the police and together they recovered 30 rubbish and carrier bags from the river near Whittlesey, mostly containing cannabis plants, roots, cuttings and buds ready to be sold.
Paul Thomas, Angling Trust’s Regional Enforcement Manager for the East of England, said: “Our volunteer bailiffs are the eyes and ears at the waterside and are trained to report suspicious activity to the police and Environment Agency to a high evidential standard. These recent finds prove how worthwhile their roles have become – they are a credit to angling and society in general.”
Paul said the drugs - and the bags they were found in - could have caused a hazard for wildlife in the area.
A spokesman for Cambridgeshire police said: “We were called at 11.13am on 27 February with reports that bags of cannabis had been found in water between Pondersbridge and Whittlesey.
“Seven cannabis plants and an additional bag of the drug were recovered.
“Yesterday (11 March) we contacted with an additional report that about 20 cannabis plants had been found underneath Beggar’s Bridge near Coates.
“No arrests have been made in relation to either incident.”
The Voluntary Bailiff Service is part of the Angling Trust’s Fisheries Enforcement Support Service, run in partnership with the Environment Agency and funded by fishing licence income.
Volunteer bailiffs are always on the lookout for signs of illegal fishing, poaching, set lines and nets but every so often they come across more sinister activity. A few years ago, bailiffs on patrol near Reading found a cache of deadly firearms, including a magnum handgun and an Uzi submachine gun.
On another occasion, an angler spotted a group of poachers and reported the registration number of a suspicious vehicle to the Angling Trust enforcement team. The information was immediately passed on to the police – and the vehicle was traced to a wanted killer on the run from mainland Europe who was tracked down and arrested.
Anyone witnessing an illegal fishing incident in progress can report it directly to the Environment Agency hotline on 0800 80 70 60. Information on illegal fishing and environmental crime can also be reported anonymously to Crimestoppers on 0800 555 111.
Anyone with information about the drugs should call police on 101.