Rangers at Colwick Country Park have warned that the repeated misuse and vandalism of lifesaving equipment could delay an emergency rescue and put lives at risk.
Lifebuoy stations around the park have reportedly been tampered with, with equipment removed or thrown into the lake.
Park rangers said they were becoming increasingly frustrated by the incidents and reminded visitors that lifebuoys must only be used when someone is genuinely in difficulty in the water.
They warned that every time a lifebuoy is moved, damaged or interfered with, it may not be available when needed and could potentially cost someone their life.
Visitors have also been reminded that swimming is not permitted at Colwick Country Park unless it is part of an organised session operated by Whole Health, where lifeguards and appropriate safety measures are in place.
Rangers monitor the country park and marina as part of their daily duties but said they cannot be present in every part of the site at all times.
Anyone who witnesses lifesaving equipment being misused, vandalism or other anti-social behaviour is asked to report it to Nottinghamshire Police by calling 101.
