Mopan River is a river in Guatemala and the Cayo district in western Belize near the border with Guatemala. The Mopan River discharges to the Belize River as the Mopan merges with the Macal River; the Belize River in turn terminates at the Caribbean Sea. The Belize River/Mopan River Catchment contains over 45 percent of the human population of Belize. A hand cranked vehicle ferry boat conveys visitors to the Xunantunich site across the turbid Mopan River. The Mopan is an important source of drinking water and other domestic use for local people living along the Mopan; however, water quality is degraded from sediment, nutrient loading, untreated sewage discharge, pesticides and other toxins.
The major source of degradation is the extensive deforestation in the upper reaches and non-sustainable agriculture. Karper and Boles have asserted: "The greater Mopan/Belize River Catchment provides a prime example of a watershed under stress from extensive non-sustainable agricultural practices that have occurred within the region over the past three decades." Slash-and-burn agricultural practices by native peoples are contributing to such watershed degradation.Xunantunich, a Mayan site, is situated approximately one kilometre from the Mopan River on high ground. Chaa Creek is another ancient Mayan site several kilometres to the southwest of the Mopan River within the adjacent Macal River watershed.