A major factor driving changes in land use and land cover (LULC) is the human population growth associated with an expanded agricultural production. In the Lambwe valley in Homabay County, Kenya, the most important reason for accelerated population growth in the last decades was the control of the tsetse fly, the biological vector of trypanosomiasis. The goal of our study is to quantify the changes of LULC in the Lambwe valley in the last 30 years, giving special attention to the Ruma National Park. We classified three Landsat images of the Lambwe valley from 1984, 2002, and 2014 by Random Forests. The Ruma National Park itself showed a diverse composition probably supported by frequent fires that lead to a short-term reduction of savanna. Nevertheless, the national park is well protected, and no profound changes could be observed. Outside the national park, agricultural area increased by about 12%, savanna and the dense forest, that used to grow at higher altitudes, decreased by about 8% and 6%, respectively. In particular, agriculture expands towards higher altitudes with steeper slopes thus leading to a larger risk of soil erosion.