Intermittent stream symbol

How to read it

The USGS symbol sheet lists perennial and intermittent streams and rivers, and a disappearing stream, among its water symbols, all in blue. A USGS report on Idaho streams sums up the convention on its 1:24,000 maps: perennial streams are solid blue lines and intermittent streams dot-dashed lines. The EPA’s description of the National Hydrography Dataset, built from those maps, says intermittent streams contain water for only part of the year, while ephemeral streams flow only after rain. Natural Resources Canada’s legend marks intermittent watercourses, lakes and ponds separately from permanent ones.

Also searched as: blue dashed line on a map, dash dot dot line, intermittent river, seasonal stream.

How reliable the line is

The same USGS report says the maps’ perennial and intermittent streams are not as accurate or consistent as desirable from one sheet to the next, and cites a Massachusetts study in which the maps had the right classification at only 69.2 percent of the sites checked. The USGS booklet also lists intermittent drainage among the symbols that have changed over the years.

Differences by country

The Ordnance Survey shows rivers and streams as blue lines.

Look-alikes

A black dashed line is a Trail symbol. Blue tufts spread over an area are a Marsh symbol.