Nature lovers said they fear a wildlife haven will be “trashed” after joggers were given permission to stage a Parkrun through the “tranquil oasis”.
Clennon Valley Lakes in Torbay, which was designated a County Wildlife Site in 2011, will host hundreds of runners every Saturday.
Friends of Clennon Lakes said the events would disturb the wildlife.
Lakes owner Torbay Council, which gave the runners permission, said it would discuss concerns with the Friends.
The three Clennon Lakes between Paignton and Goodrington are home to kingfishers, egrets, herons and many other species “not seen anywhere else in Torbay”, said the Friends.
The Parkrun, which already takes place in the area and draws up to about 400 runners every Saturday, was given permission on 19 August to run around the lakes, but has not used them yet.
The runners’ usual 5km (3.1 mile) route starts at a nearby cycle track and skirts the lakes area.
The Friends won £10,000 from Tesco to restore walkways around the lakes to open them up for disabled people.
“The council has given the park runners permission to use our paths as a running track,” said Friends chairman Mike Langman.
“But they were not put in as a running track, they were put in so everyone could enjoy nature and the tranquillity of the place.
“The wildlife will be disturbed in what is the most significant wildlife reserve in Torbay, there are species there that you will find nowhere else in the area.”
Mr Langman, a birdwatcher for 45 years, said the Friends were not consulted on the move.
He also accused the council of reneging on a promise to dredge the lakes of silt, a “vital” move to maintain the nature reserve.
A Torbay Council spokesperson said the authority was aware of the concerns and was “happy to assist in facilitating talks with all those involved who use the Clennon Valley area to hopefully come to an agreement on the best next steps for everyone”.
It was also due to meet the Friends in October “to discuss the desilting works”.
No-one from the Parkrun was available for comment.