The study looked at water pollution in four rivers near the Yellow River estuary. Water samples were collected at different times to measure pollutants like nutrients, COD, chlorophyll, and petroleum. The rivers were found to be seriously polluted, mainly with nitrogen, phosphorus, ammonia, and petroleum. This pollution led to eutrophication in the Bohai Bay, causing harmful algal blooms. The pollution by nitrogen and phosphorus has worsened over time, while petroleum pollution has remained stable. Overall, the water quality in these rivers is not good, impacting the coastal ecosystem.