Concerns have been raised after eggs and flour bombs were launched at participants and ducks during the traditional Boxing Day raft race in Matlock.
Some spectators are said to have thrown eggs at people travelling down the River Derwent on home-made rafts as well as targeting ducks and geese.
The throwing of eggs has happened for a number of years but calls are now being made to stop it before someone gets seriously hurt.
Stephen Eyre, of Derbyshire Association of Sub Aqua Clubs, which organises the event, said: “We do not mind a bit of flour or water but then some bright spark a few years ago started to throw eggs and it has continued from there.
“People who throw eggs need to understand that it is not allowed and that it could blind someone.
“Some people think it is funny but it is not.”
As many as 6,000 spectators attended the 54th annual race as 400 people on more than 40 rafts raced across the three-and-a-half mile course on the River Derwent from Matlock to Cromford Meadows.
A spokesman for the Environment Agency in the East Midlands said: “As part of the race, some spectators throw flour-filled plastic bags at the raft racers. We are concerned about these plastic bags entering the watercourse as they pose a threat to local wildlife and the environment. This year there have been sightings of water birds near the floating flour bags following the Boxing Day event.
“In advance of next year’s race, we are working with partners to consider alternative options to help limit any environmental damage caused.”
The race raised a total of £1,910 for the Royal National Lifeboat Institution. The winning teams were: 1. Las Vegas 2. Black Swan. 3. Oktoberfest.