Originally it flowed into the River Callan at Fairlawn Bridge, but was diverted into a cut excavated in 1851–4, which intercepts it at a point 2 km above the former confluence and conveys it directly to the Blackwater just above Verner's Bridge.
[2] The "Old Course of the Tall", from the interception down to Fairlawn Bridge, is so named on maps of the time,[3] but it is unnamed on more recent OSNI maps,[4] and may have been partially filled in.
A second cut, completed in 1855, partly diverted the Callan, by means of a weir at Clonmain Mill near the junction of the Summerisland Road and the Cloveneden Road, to the Tall at a point 0.3 km above the latter's own diversion,[2] but the bulk of the Callan has continued in its original course.
[4] In common usage, the name "Tall River" is now extended to include the first cut, all the way from the interception down to the Blackwater, but OSNI maps attach the name only to the part upstream from the interception.
This article related to a river in Northern Ireland is a stub.