Nottinghamshire Police in Sherwood issued the warning as hot weather hit the region.
Police said:
During this period of hot weather, we continue to receive numerous calls and complaints regarding the lakes in Hoveringham and the river front at Gunthorpe, which relate to parking and swimming.
Individuals are clearly ignoring the obvious dangers of swimming in deep and fast flowing waters with reports of people swimming in the lake and jumping off the bridge into the River Trent.
We would like to remind people the dangers of open water swimming which can have deadly consequences and is highly dangerous.
The water may look calm on the surface, but there may still be strong undercurrents that could pull even a strong swimmer under.
The water may also feel relatively warm on the surface, but just a few feet below can be icy cold even in the hot weather and can very quickly cause severe cramp and hypothermia.
Young people often misjudge their swimming ability – they may view a river or lake as a tempting means of cooling off during a hot spell of weather, but fail to appreciate the harmful effects that the cold water can have on their stamina and strength.
Due to these dangers, we are urging people, particularly children and teenagers, not to swim anywhere other than in purpose-built and supervised swimming pools.
We would also urge parents to be aware of where there children are as we are seeing many groups of teenagers and children gathering in these locations.
Parking is also creating a significant issue, where visitors to the locations appear to be abandoning their vehicles on the road side thereby causing obstructions and restricting access.
We would ask that if you are visiting the locality ensure that you are parking in a location which is suitable, appropriate and considerately for other road users.
Be respectful for the area and its residents and pick up your litter.