The Cornwall Wildlife Trust is concerned about dolphins being harassed after reports of large numbers of the creatures around west Cornwall.
Up to 1,000 of the animals have been sighted around the coast in the past five days.
The trust said a number of skippers had been annoying the animals, and were unaware of how to react around them.
Dolphins, harbour porpoises and basking sharks are protected species. Harassing the creatures is a criminal offence.
The trust said the Marine Creatures Code of Conduct existed to protect marine wildlife. The code states that boats should stay at least 100m (330ft) away from dolphins.
It also says if the creatures approach a boat, the engines should be switched to neutral.
The penalties for ignoring the code can be fines of up to