Not long ago acid rain, which forms around airborne oxides of sulfur and nitrogen and falls to earth with rain and snow, was a major threat to northeastern Minnesota lakes. But the 1982 Legislature passed a law, the first of its kind in the world, that led the MPCA to develop an acid-deposition control plan. Today acid rain has been held at bay by reductions in acid-forming emissions here and in other states. Despite the environmental successes of recent decades, the northland faces continuing environmental challenges. Mercury makes fish unsafe to eat in too many lakes.
Some smaller towns lack adequate wastewater treatment.
Among the foremost challenges for the Arrowhead is rapid development. The north shore of Lake Superior, for example, is growing faster than anywhere else on the big lake. Other lakes in the northeast are feeling the same pressure. The density of lakeshore development has to some extent been limited by available wastewater treatment. Consequently homes and businesses outside of cities have relied on septic systems, which need space for drainfields necessary to protect lakes and ground water.