Rainwater runoff from urban areas in Shenzhen Bay, southern China, carries a lot of nitrogen and phosphorus into the water, causing eutrophication issues and increasing the risk of red tide. A study used a model to show that 60-80% of pollution in the bay comes from rainwater runoff, leading to short-term pollution spikes. Nutrient salts from runoff affect algae growth differently than in the city, impacting chlorophyll-A levels in the bay. The farther from the city, the less impact runoff pollution has on the water.