Wied ta' Għajn Rihana is a broad flat-floored valley located to the north of the Victoria Lines fault and spans three local councils: Mġarr, Mosta and St Paul's Bay. The valley system constitutes one continuous wied with two main tributaries - Wied ta' Sejkla and Wied ta' l-Arkata. Wied ta' l-Imselliet and Wied tal-Ħżejjen form the upper parts of the wied, joined by Wied ta' Sejkla at il-Ħżejjen. The valley then continues as Wied ta' Għajn Mula that is joined by Wied ta' l-Arkata at Ġnien Nixxuf. The downstream part of this valley, joining Wied il-Għasel at Għajn Rihana, is located on the opposite side of Burmarrad Road and is locally referred to as Wied ta' Għajn Rihana.

Valley-sides and watercourses within valley systems present different environmental conditions that are exploited by distinct vegetation communities. Vegetation communities associated with valleys can thus be divided into those that characterise the valley-sides or valley-slopes and those that are associated with the watercourse. During the winter months the watercourse of Wied ta' Għajn Rihana holds a substantial amount of freshwater, supporting biotic communities that are typical of local watercourses.

The valley banks support limited stretches of deciduous trees that are generally associated with watercourses (riparian woodlands) and are quite rare within the Maltese islands.

Mepa scheduled Għajn Rihana valley system as an Area of Ecological Importance and Site of Scientific Importance as per Government Notice No. 226/06 in the Government Gazette dated March 10, 2006.