Complex sentence: Lake Koocanusa is the name of the impoundment reservoir behind the dam; it extends 90 miles (145 km) upriver from the dam and has a maximum depth of about 370 feet (110 m).
Split into simpler sentences: Lake Koocanusa is the name of the impoundment reservoir behind the dam. It extends 90 miles (145 km) upriver from the dam and has a maximum depth of about 370 feet (110 m).