Canadians are proud of the Great Lakes, and for good reason—they supply two large countries with a lot of fresh drinking water, support irrigation and other agricultural activities, and are crucial in shipping and transportation in the area. Plus, they’re great for sailing, swimming and watching the sunset. “Lakes are great indicators of what’s going on in the watershed,” says Sapna Sharma, an associate aquatic ecology and limnology professor at York University. “They give a good idea of what environmental degradation may be happening on land.”