This paper is the result of hydrogeological survey engineering.

Objective Although lake resources in Henan Province are relatively scarce, their functions are irreplaceable. They not only carry the basic livelihood guarantee functions of urban and rural water supply, agricultural irrigation, but also play an ecological barrier role in flood regulation, species conservation, water quality purification, etc. Strengthening the defense line of water ecological security is the key to promoting regional sustainable development. Scientifically assessing the quality of lake water environment can provide theoretical basis and technical support for lake water pollution risk warning and water environment governance.

Methods This study takes typical natural lakes in Henan Province, including Hei Lake, Liu Lake, Longhu in Huaiyang, Nanhu in Suiyang, and Beihu in Suixian, as the objects, using single factor evaluation method, comprehensive pollution method, and improved comprehensive pollution index method based on entropy weight method to evaluate the water quality status of each lake area. The evaluation results of the three methods are compared and analyzed, and the most suitable evaluation method is selected.

Results The water quality of Hei Lake and Liu Lake met the water quality requirements of the water source protection area, both meeting the Class II water standard. However, the urban lakes of Longhu in Huaiyang, Nanhu in Suiyang, and Beihu in Suixian were greatly affected by human activities, and the monitoring area was in Class IV or V water. Total phosphorus (TP) was the main pollutant, exceeding the standard severely. Total nitrogen (TN), chemical oxygen demand (COD), and fluoride (F^–) all showed varying degrees of pollution.

Conclusions Comparing three evaluation methods, the comprehensive pollution index improved based on entropy weight method comprehensively considers the water pollution characteristics of each lake area and the impact of different pollutants on the regional water environment. The evaluation system is more scientific and reasonable, the evaluation results are more distinguishable, and can better reflect the real water quality situation.