An environmental and research group is looking for the public to help name two dolphins that live in the Potomac River.

The deadline for the naming contest, which is being run by the Potomac-Chesapeake Dolphin Project, ends May 24. The two dolphins that need names are now called “D1” and “D2″ and are believed to be mature adults.

The dolphins have been sited swimming along the Northern Neck, in the Vir-Mar Beach area.

Officials with the Potomac Conservancy said there’s roughly 1,000 dolphins have been identified swimming in the Potomac River and Chesapeake Bay. Dolphins migrate from the Atlantic Ocean and spend the summer in the Potomac, where they birth and raise their calves.

Experts said they believe that cleaner water is helping bring dolphins farther up the river. They’re typically seen in brackish waters where the Potomac empties into the Chesapeake, according to the Potomac Conservancy.

In the 1980s, dolphins had been seen regularly, experts said, near Indian Head, Md., and at times as far up river as Alexandria.

The naming of the dolphins is part of an effort by the Potomac-Chesapeake Dolphin Project, which studies their breeding and mating habits, eating patterns and migration. Since 2015, they’ve named roughly 300 dolphins.