The researchers looked at how agricultural land affects the water quality of rivers flowing into Erhai Lake. They used maps and statistics to see how different types of farmland impact the water. They found that areas with more farmland had higher levels of pollutants like nitrogen and phosphorus. Forest land, on the other hand, helped lower these pollutants. Overall, the type of agricultural land near the rivers had a big impact on the water quality, with farmland increasing pollution and forest land reducing it.