Final answer:
Building over fisheries and nutrient runoff can cause a decline in fish populations and eutrophication, seriously reducing water quality and harming aquatic organisms.
Step-by-step explanation:
The consequences of building over fisheries and nutrients running into fisheries can lead to a decline in fish populations and eutrophication. Eutrophication occurs when excess nutrients, particularly nitrogen and phosphorus, from sources such as agricultural runoff and sewage, lead to a proliferation of algae. The algae bloom depletes the oxygen in the water, causing serious reductions in water quality and can result in the death of fish and other aquatic organisms. Additionally, building over fisheries removes habitats for fish and can interrupt nutrient cycling in these ecosystems. While decreased fishing can initially help fish populations rebound, the overall impact of habitat destruction and nutrient pollution can severely damage aquatic ecosystems.