Blackadder Water () is a river in Berwickshire in the Scottish Borders area of Scotland, forming part of the River Tweed system. The water reached a height of 2.84 metres at Mouthbridge, which was its highest level ever recorded on Tuesday 22 October 2002 at 2:45pm.
Etymology
Adder may be derived from Brittonic *ador or *edir, or Old English ǣdre, possible ancient hydronymic terms derived from an Indo-European formation meaning "a watercourse, a channel" (compare River Etherow). meaning "long water".