Built in 1923 as a 2-8-2 by Davey Paxman of Colchester and designed by Henry Greenly, it was designed to haul both stone and passenger trains, however soon found more use on passenger traffic. It was originally fitted with Lentz poppet valve gear, but this didn’t prove to be successful. It was painted works grey in 1924, then LMS red with black and straw lining to 1927. It was then repainted mid green with black and yellow lining during a rebuild in 1928 by the Yorkshire Engine Co, when the original valve gear was replaced with the current Walschaerts valve gear. At the same time, the loco received a Poultney steam tender, making the locomotive a 2-8-2-0-8-0. This proved unsuccessful and was soon removed, instead being utilised nearly forty years later as part of the second River Mite, after languishing at Murthwaite. The locomotive was out of use from 1940 to 1952, survived into the preservation era and was repainted in a new livery of LNWR black in 1967 and received a new tender in 1970. In 1983, the Esk was fitted with a gas-producer boiler and received an award from British Coal, however this has been out of use since 2001. The locomotive has visited the Romney, Hythe and Dymchurch Railway several times and was a predecessor to that railway's Greenly Pacific locomotives. The engine is currently in Blackberry Black of the LNWR with red, off-white and black lining.

In 2013, River Esk was undergoing an overhaul in the workshop at Ravenglass when the facility was destroyed in a fire. Staff and volunteers managed to save the frames and some other components from the flames, but the majority of River Esk’s parts were damaged beyond repair. Following completion of the new workshop in 2015, River Esk was rebuilt at Ravenglass with a new tender based on the one provided for Whillan Beck, and improvements to her exhaust system. She returned to steam in 2018, and remains in regular service.