Agricultural run-off significantly impacts aquatic ecosystems by introducing excess nutrients, particularly nitrogen and phosphorus, into water bodies. This often leads to eutrophication, where rapid algal blooms deplete oxygen levels, threatening aquatic life. Additionally, pesticides and heavy metals from run-off can be toxic to fish and other organisms, resulting in a decline in biodiversity. The overall health of these ecosystems is compromised, impacting water quality and potentially leading to the collapse of local fisheries.