A stream or reach of a stream that ﬂows year-round in a well-deﬁned channel is known as a perennial stream, also called a permanent spring. The Army Corps of Engineers deﬁnes a perennial stream as one that ﬂows 365 days in a typical year. The stream ﬂows when it receives signiﬁcant amounts of water during wet periods; when it receives groundwater discharge from below, reaching the surface through springs or seeps; or when it receives long-term water from melting snow and ice. Perennial streams can dry up, though, particularly during extended periods of drought, damaging the life within them that depends on constant ﬂow. The distinction between perennial and intermittent streams is often a subject of controversy in localities, as speciﬁc conservation ordinances often set exact guidelines for a property with a designated perennial stream.