Mercer Island beats Bellevue | Girls prep water polo The Mercer Island girls prep water polo team traveled to play Bellevue in a conference match on Wednesday, April 24. By Megan Managan • April 25, 2013 1:50 pm The Mercer Island girls prep water polo team traveled to play Bellevue in a conference match on Wednesday, April 24. Mercer Island won the game 10-2. The Islanders will travel to Portland this weekend for the annual Rose Cup tournament.