Marine biologists were standing watch on Tuesday over a young whale that lost its way in New York harbor and nearly wandered into a narrow waterway notorious for industrial pollution. The animal, described as a juvenile minke whale about 15 feet long, was cruising around Gowanus Bay, the outlet from the mile-long Gowanus Canal in Brooklyn. It appeared to be in good health and not distressed, said Kim Durham, rescue program director for the Riverhead Foundation for Marine Research and Preservation. The foundation, based in Riverhead, N.Y., specializes in cases involving whales, dolphins, seals and sea turtles. Durham and other experts were dispatched to the scene after the whale was spotted early Tuesday. A television news helicopter videotaped it leaping out of the water, a behavioral trait common to whales of the baleen species. The whale's playground was in waters hemmed in by docks and a large oil depot at the exit from the famously polluted canal, but Durham said she was not unduly concerned that it would be affected in the short term by anything in the water. Durham said she was glad to note that the whale was not swimming in tight circles or exhibiting other behavior that might be indicative of disease. She said the whale would be monitored overnight, with the hope that it might decide on its own to leave the area and swim out into the harbor, where the water is deeper. "My main concern is not what it is doing but simply why it is here," Durham said in a telephone interview. "This is not really an environment conducive to its good health." The US Coast Guard and a police harbor patrol boat were standing by but didn't plan to take action unless it was necessary. Whales are a rare sight in New York harbor, and it was not immediately known when a previous sighting of a live whale last occurred. A New York Aquarium official, Fran Hackett, theorized that the whale followed a school of fish into the Gowanus area. "It's just swimming around in there, and reasonably well," she said in a telephone interview. The Gowanus canal, named for a native American group that once lived in the area, runs about a mile from picturesque Boerum Hill in south Brooklyn to the bay in Red Hook, a quaintly rundown harbor community where grain ships once loaded cargo for Europe and shipyards turned out ferry boats and fancy yachts. The last reported incident involving a whale was the discovery in 2000 of a dead whale floating in the harbor between Brooklyn and Staten Island, apparently the victim of a collision with a ship. In 1993, an ailing whale was recovered off the north shore of Long Island Sound and was nursed back to health during eight months at the New York Aquarium in Coney Island.