1. Due to high temperatures and an overgrowth of algae in many freshwater lakes, numbers and sizes of crabs have declined.
2. Overgrowth leads to oxygen deprivation, starving most other aquatic organisms of oxygen.
3. Nitrogen and phosphorus discharged into the lake has caused an overgrowth of algae, further deteriorating the water quality.
4. A sudden overgrowth of blue algae polluted the daily water supply for millions of lakeside people.