Welcome to Martha’s Vineyard, Mr. President - but don’t go in the water! President Obama, who took a plunge in the Gulf last week to show Americans it was safe to swim the oil spill-plagued area, arrived on this supposedly pristine island yesterday in the midst of a rash of bacteria-induced beach closings. Portions of Tisbury Great Pond, the salt-water lagoon fronting the first family’s vacation estate Blue Heron Farm, were closed earlier this week due to high levels of enterococci, an indicator that the water is contaminated with fecal coliform bacteria. Ew. High levels of enterococci can cause skin...