Reports of dead fish — most of them yellow perch — on four lakes in northern Maine have prompted questions from the public. While it might seem unusual, the official word from the Maine Department of Inland Fisheries and Wildlife is that the fish die-off is natural. It shouldn’t cause concern. Frank Frost, the department’s fisheries resource supervisor for the Fish River Lakes Region, said a large number of fish have died on Long Lake, Cross Lake, Square Lake and Madawaska Lake. “[It’s] certainly not a regular event, like annually, but fish kills do happen on an irregular basis,” Frost said.