Shopping trollies lay abandoned and litter was found scattered under a Thetford bridge over the bank holiday weekend.
Members of the Thetford River Group collected a large amount of waste on Monday, May 2, from a short section of the River Thet under the London Road bridge in the town.
Sean Ready, founder of the group, said: "We've noticed a rise in trollies being thrown in rivers since the price of fuel went up.
"More people are walking to collect their shopping instead of driving or getting a taxi and then disposing of the trollies once finished."
Fellow volunteer, Claire Higson, added that she believes the group are making a difference after noticing a reduction in the amount of rubbish found.
She added: "It's dangerous for people on canoes and kayaks.
"I can't understand the thinking behind putting a trolley in the river, you might as well use it for the next time.
"We clean the river once or twice a week. There's a lot of rubbish but there is less than there was."
Thetford River Group, which now has 10 volunteers, was founded by Mr Ready in 2014 and has grown to become a group who conduct river crime monitoring and check the water quality of the town's rivers.
Mr Ready added: "People need to use the provided bins and there are enough of them in town.
"It's just laziness really."
The majority of the rubbish was from cans and bottles of alcohol that had been dumped and it has been an ongoing issue in the area for months.
Ms Higson added that it was important to "educate people" in order to stop similar incidents happening.
She said: "80pc of plastics that end up in the sea come from the rivers.
"If you don't pick up the plastic then it will disintegrate and go into the North Sea - it's a constant cycle."
Neighbour Colin Woods thanked the group for their help but urged people in the town to do more.
He said: "Another amazing job done by Sean and the Thetford River group clearing our river and the surrounding area.
"But come on Thetford, let’s start taking a bit more pride in our town and take our rubbish home or find a bin.
"Let's appreciate the beautiful area we live in and all play our part to keep it tidy."
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