About 10 miles of popular beaches at the southern end of Monterey Bay are closed while officials test a mysterious brownish goo spotted floating offshore. Beaches from the Monterey harbor to the town of Marina were closed after the Coast Guard spotted the glop in a mile-long, quarter-mile-wide swath. A sample of the substance, described as slippery or sudsy, has been sent to the state Department of Fish and Game's lab for testing. The Coast Guard and the county also are testing samples. "If it's a hazard, it involves a cleanup," said Walter Wong, county director of environmental health. "If it isn't, no harm is done" by closing the beaches.