A whale has been spotted in the Elizabeth River in Chesapeake, Virginia and it's been behaving erratically. The Coast Guard has issued a statement telling boaters to avoid the whale for the time being. They told boaters that they should not approach the whale or try to feed it.

The whale is approximately 30 to 40 feet large, the Coast Guard estimates. It was found yesterday, on Monday August 19, 2014, swimming in the Elizabeth River, a river that is usually heavily trafficked by boats. The Elizabeth River flows into the Chesapeake Bay. The Coast Guard warned boats to be careful to avoid the whale if they see it swimming above the water.

Mark Swingle, a member of the Virginia Aquarium & Marine Science Center says that the species of the whale has not been discovered yet, but that it could be a sei whale. Adult sei whales weigh up to 20 tons and are about 45 to 65 feet long.

The whale's erratic behavior could be caused by illness, Swingle says.

One person who reported seeing the whale is Brook Smith, the captain of the American Rover, who saw the whale on Friday August 15. He said that he saw the whale swimming in circles for about 20 minutes from his boat.

"It seemed to be kind of swimming in circles -- no particular direction. I'm not a whale expert, but it looked ill," Smith said.

It is unusual for sei whales to swim in waters so close to the coast line. They typically prefer deeper waters. It's also rare for a sei whale to be spotted by humans.

"It's not in a normal place," Swingle said.

The Virginian-Pilot, a newspaper, uploaded video footage of the whale. You can watch it online here. The Virginia Aquarium has requested that any sightings of the whale be reported to them. They can be reached at (757) 385-7575.

Sei whales are an endangered species. The World Wide Fund for Nature says that sei whales are a priority species, meaning that they are crucially important to their ecosystems. They live in all oceans around the world. They typically feed by sucking prey out of the water through its teeth. The whales prefer warmer waters but currently populate oceans worldwide.

There is currently a $50,000 fine in place for threatening a member of an endangered species. Boaters and individuals should not attempt to approach the whale.