The article looks at water quality in Yitonghe river in 1994 and 1999 to understand pollution levels and changes over time. It analyzes why the water is polluted in the river. The main goal was to figure out how pollution affected the water quality over those years. Researchers checked the water quality in different years and found that it got worse over time. They studied the reasons behind the pollution, aiming to understand what caused it to happen. They found that the water was indeed getting more polluted, and they wanted to know why.