A pod of dolphins swam right up to several small boats floating in a calm river, much to the surprise of young sailors.

The playful mammals happily came up close and circled each of the dinghies and other vessels, feeling undisturbed by their encounter with humans.

These aquatic creatures stayed close to the boats for more than an hour while sailors searched for fresh fish.

Dolphins often appear along the coastline and occasionally enter river systems. They usually migrate in pods of between two and 30, while some superpods are found to comprise 100 or even thousands of dolphins. These pods help dolphins stay together, support each other, and collectively hunt for food as a group of social animals.

The latest large pod entered the River Dart between Dartmouth and Kingswear, Devon in England, and raced for more than an hour on June 26. This overjoyed the young sailors.

At least nine dolphins swam between two boats, according to one photograph taken by Andy Kyle of the South West News Service. The sailors carefully controlled their speed and kept a safe distance from the dolphins, who happily swam close to their vessels. The water mammals, which seemed exceptionally friendly, remained unfazed even after an enormous ferry passed by.

According to the Sunlight On Water website, dolphins can rapidly swim at speeds of between 11 and 12.5 kph (6.8 and 7.7 mph) for extended periods of time. As their speed increases, they can jump higher above the water surface, which helps them conserve energy. Some of the world’s fastest dolphins have achieved speeds of up to 26.3 kph (16.3 mph) and jumped continuously while being followed by a speedboat for about 1.5 km (0.9 miles.)

Faster speeds are possible when a boat’s bow wave carries dolphins along, giving them a free ride. Dolphins can even reach speeds exceeding 15 knots (17 mph) in short bursts, such as preparing for a great leap. However, they cannot maintain this pace for extended periods. The optimal travel speed for dolphins is actually between 6 and 8.2 kph (3.7 and 5 mph).

Dolphins are self-aware creatures, according to a study conducted at the Wildlife Conservation Society’s New York Aquarium. This profound cognitive ability was previously only recognized in humans and large apes (Reiss & Marino, 2001).