For a variety of reasons, the Baltic Sea is considered one of the most polluted seas on Earth. Nutrient runoff stimulates algal blooms and depletes oxygen levels, leaving the water dark and murky. Urban waste and industrial pollution, which frequently find their way into the sea, are impacting its ecosystem. Fishing (purportedly too intensive) and climate change are gradually "showing" their long-term effects. With the populations of fish species native to the Baltic Sea, such as Baltic cod, (reportedly) in decline, the aforementioned fishing industry in the region is being seriously affected.