It added there had been an increase in the number of dolphins spotted in Cornish waters and a rise in waterway activity with recreational boats over the past 10 years.
“Whilst this can lead to spectacular encounters for us, it also brings them into our very busy coastal waterways,” Rebecca Allen, marine conservation officer at the trust, said.
“We urge water users to please keep at a sensible speed and follow government guidelines if they do see marine animals: reduce to slow, ‘no-wake’ speed and keep to a safe distance – at least 100m (328ft) away.”