The existence of the lake is very important for the Balinese people, as a source of drinking water, as well as in the spiritual aspects of Hindu religion. One of the lakes on the island of Bali is Lake Buyan. Geographically, it is located in Pancasari village, Sukasada district, Buleleng, Bali. The Bali Provincial Public Works Department ' Data shows that in the last 15 years from 1999 to 2015, there is an increasing decrease in the area of the lake. In 1999 the area of the lake was recorded at 439 Ha and shrunk in 2015 to 376 Ha. One of the factors that affect the area of the lake is the occurrence of soil erosion. In this study, a simulation model was developed to predict landslide/soil erosion conditions in Lake Buyan. This avalanche simulation model is based on the USLE (Universal Soil Loss Equation) formula. It is stated that erosion is influenced by soil erobility, rain erosivity, steepness of slopes, tillage, and soil conversion. Based on the developed simulation model, it is shown that the biggest influence that affects the landslide in Buyan Lake is rain erosivity. Rainfall predictions based on rainfall data for the last 10 years show that the rainfall is getting smaller. On the one hand, it will bring the advantage that the quantity of landslide erosion in the next few decades will be smaller. Based on the simulation model, predictions show that in 2020, 2030, 2040, and 2050 the amount of erosion is 116.5 tons, 74.23 tons, 18.62 tons, and 7.5 tons. On the other hand, this is very worrying because rain is the only source of water for Lake Buyan.