Last week in Helford Passage Cornwall, England I spotted a short stubby, black and white bird in the salt water about 3 feet from the shore. It dived under and propelled itself underwater like a torpedo sometimes popping out of the water (presumably as it chased a fish). when it surfaced it popped up like a cork (which is a characterstic of a Little Grebe I understand) but this bird was no more than 10 inches long and black and white. I cannot identify it. Can anyone help?