Eutrophication

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Eutrophication is when to many plants grow in a lake or near one and the plants take up all of the oxygen. This causes fish in the great lakes to die. Before the Europeans arrived in the great lakes, they were mainly oliggotrophic lakes, meaning they contain little plant nutrients (killing lots of animals) and were continuously cool and clear due to their immense size and depth. After Europeans, they began farming with pesticides which ran off into the lakes causing plants to grow and decreasing oxygen for animals.