The River Ems is a much-sluiced, chalk stream that is located in the far west of the county of West Sussex, England. It flows from Stoughton in the north, then southwest through Westbourne to Emsworth in the South. The last , of this river, delimits eastern Hampshire, before flowing into the sea at Chichester Harbour.
The river was so named, the "Ems", by a chronicler in the Tudor period.
Over the centuries various cartographers and chroniclers have suggested a variety of sources for the Ems. According to research by David J. Rudkin the River Ems has its source about east of Stoughton.
The River Ems, is a chalk stream that has a catchment area of over , and its upper reaches drain the South Downs. It is one of eight water bodies that are designated by the Environment Agency, as being part of the Western Streams Operational Catchment.
Although, the lower and some of the middle reaches of the river, equating to (approximately) the last , flow throughout the year, the rest of the middle as well as the upper reaches of the river naturally stop flowing during dry spells.
Increasingly, sections of the river stop flowing during dry spells; this is largely due to the level of abstraction in recent years. The river has several minor tributaries in the upper and middle reach. There are some significant tributaries at the lower reach of the river.
From its source the River Ems runs past:
It is sometimes thought that the town of Emsworth derives its name from that of the River Ems, this is not correct as before the 16th Century the stream was originally called the Bourne. The river was renamed by the 16th century chronicler Raphael Holinshed. Many of the towns and villages that the River Ems runs through or past still have Bourne as a suffix. e.g.:Westbourne.