Polluted waters have destroyed otters habitats. © Lee Brun   Threats to Otters Population estimates are difficult to obtain, and densities of river otters in a given area usually low because individual males hold large territories. Nevertheless, several reasons clearly underlie the overall decline in river otter populations: • Habitat destruction. Over the last 150 years, expanding human settlement has transformed the central United States. Population growth has resulted in waterways being developed for recreational and industrial uses, and land near rivers being taken over for housing or farming. All of these practices have greatly reduced the river otter's natural range. • Water pollution. Otters are extremely sensitive to environmental changes, and tend to avoid polluted or disturbed waterways. Their disappearance from West Virginia and parts of Tennessee and Kentucky has been attributed to increased acidity of groundwater due to mining operations. Industrial effluents (such as mercury) and runoff from agricultural operations (like silt and pesticides) are also culprits.      2 of 6