Bottles, cans, bags and other litter have been washed up in Watermead Park by the recent floods.
High water levels led to the River Soar picking up more litter along its route through Leicester and much of it ended up being washed over the country park.
Andrew Jackson, 42, who lives in Thurmaston, reported the issue to Leicestershire County Council, which is responsible for the northern part of the park.
He said he was not happy with the response he got from them.
He said: "I was walking around the park after the floods last week and it's a tip.
"There are nappies and bags and all sorts of rubbish that's been washed up.
"I rang the county council and they weren't interested. I was told that there would probably be a litter pick at the end of March.
"It's supposed to be a nature reserve. Dogs and birds can get hurt by that litter.
"I'm not normally one for complaining but you see a mess like this and wander what sort of nature reserve it's supposed to be.
"No one seems interested in cleaning it."
John Tompkins, 61, of Anstey, visits regularly and also canoes through the park on the river.
He said the river was regularly affected by the litter being washed down and that floods led to a big increase in the amount of litter on the park.
He said: "You do find a lot of litter along the route of the old River Soar and I always see a lot more after floods.
"When the water gets very high you get rubbish in the trees and it's all the things the river has picked up downstream in Leicester.
"I saw a bike in a tree once.
"I think the council does an okay job and there are people like myself who will pick up odd bits of litter. People are proud of the area."
A Leicestershire County Council spokesman said dangerous items would be removed promptly and other litter would be cleared "over the coming months".
He said: "Maintaining Watermead Country Park in a safe and clean condition is a high priority for our country parks service.
"We continually need to litter pick as a result of material being brought into the park by the Grand Union Canal and the River Soar and this is work is done by volunteers and county council staff.
"The amount of material collected each week is significant and is removed from the site by a waste disposal contractor following collection but is accentuated when the watercourses flood. This has happened an exceptional four times this winter and created a backlog which will be cleared over the coming months.
"When we become aware of large or dangerous items, we seek to remove these promptly."
