BROOKLINE – State Fish and Game officials have been warning people about thin ice all winter, and the dangers became spectacularly clear last Friday when an extralarge bob house went through the ice at Lake Potanipo. No one was injured, but it took the owner and his friends two days to clear away the strippedout camper that was being used as an ice fishing shelter, Brookline Police Chief William Quigley said Monday. Police notified all emergency services, the chief said, and luckily there were no fuels or other substances that would have contaminated the water. The bob house was about 150 feet from the town beach, near what is called the First Cove. People were still picking up debris until around noon Monday. There had been a few other bob houses on the lake, but they were all gone by Monday afternoon, Quigley said. "There is an awful lot of open water," he said. Fish and Game advises people who want to ice fish not to guess about ice thickness and to use an auger or axe to make test holes. Look for 4-6 inches of solid bluish-black ice, which can support a few "well-dispersed" people, while 8-10 inches can support off-road vehicles.