What's Killing the Fish?

Lake Gordon, a large recreational lake is New Jersey, is home to large amounts of fish. However, residents near the lake are starting to notice that unusual amounts of dead fish are appearing on the lake. EPA investigators found that toxic substances were not present in the water, leaking of sewage into the water has caused an increase in the number of aerobic organisms in the sediment of the lake bed along the south shore, and that runoff of detergents and household fertilizers has caused an excess of algae around the south shore. From the data and graphs presented to me on pages 2, 3, and 4, I believe the algae accumulation in the lake is the cause of the dead fish. It could be because the algae are using up vital oxygen sources that the fish need to survive. Table A on page 3 shows the amount of dead fish increase as the number of algae cells increase. This shows that the algae and fish are competing for oxygen, and the fish are losing. Also, oxygen levels in the lake slowly decreased over a 3 day period, as shown by Table B on page 3. This possible algae-fish competition might have contributed to that. Furthermore, the human residences on the lake south shore may contribute to this fish crisis, because the majority of dead fish are amassing near the homes, as shown in Diagram C on page 4. The residents’ runoff of fertilizer and detergent likely caused the algae growth, leading to more dead fish, and also explains why the dead fish are gathering near the south shore. A reasonable solution to this ecological issue would be for the residents to be careful in their detergent/fertilizer usage, and also to create some sort of subterranean barrier between the houses and the lake, so that more pollutants cannot contaminate the lake and create algae via runoff from the residential area. This solution might change my “% Saturation Dissolved Oxygen” graph because with the algae cells reducing in number, there will be less organisms competing for oxygen in the lake,