Police have received multiple reports of youths entering the water at the reservoir in Netherton as the weather continues to heat up.
The behaviour has been described as "unacceptable" and police are working with owners to help tackle to issue.
A spokesperson for Dudley Police said: "We want everyone to have an amazing but safe time during this weekend's scorching weather, however, we've had multiple reports of youths trespassing, entering the water after alcohol consumption and causing criminal damage at Lodge Farm Reservoir, Netherton.
"Please be aware that this behaviour is unacceptable and we are working in conjunction with the owners and other agencies to remedy this anti-social behaviour.
"If you know of any youths causing ASB please don't hesitate to contact us via 101 or 999 in an emergency."