Taking an almost straight south-flowing course, the Rom passes under the London Loop and experiences a drop of 24 metres (79 ft) in elevation before it enters the ringroad enclosed town centre of Romford where it becomes underground in a culvert, a man-made tunnel, at 16m AOD.

[4] The name of the river is first recorded in the 13th century as le Markediche, meaning 'boundary ditch' and referring to the ancient boundary between the parishes of Dagenham and Hornchurch which later gained borough status.

[4] Throughout the northern section, where the Rom starts, in the north western part of the London Borough of Havering its valley has been designated as a Site of Importance for Nature Conservation[5] The river contains unbranched bur-reeds (Sparganium erectum and Sparganium emersum) and fool's watercress (Apium nodiflorum), and supports water voles, kingfishers and reed buntings.

[6] Further downstream, the Beam Valley is a mixture of woodlands, acid grassland, ponds and marsh areas, a habitat for many types of wildlife.

The London Boroughs of Barking and Dagenham and of Havering plan to develop the area to improve the conservation interest and to create new opportunities for recreation and education.