Wied il-Kbir and Wied Għomor are two interconnected valleys bordered by the local councils of Swieqi, San Ġwann and St Julians. These valleys have a north-easterly gradient, with Spinola Bay the final discharge point.

The valleys originally used to discharge rainwater run-off into a saltmarsh but this was obliterated by physical development.

This valley system is composed of lower coralline limestone, rendering the valley beds very permeable. The relatively rapid infiltration of surface water in the valley beds improves the drainage capacity of the area and reduces run-off losses to the sea as this water finds its way to the mean sea level aquifer. The slopes of the valley have a significant aesthetic value and are of scientific importance in terms of hydrogeology and geomorphology.

Three tributaries constitute the beginning of this valley system: Ta' Wied il-Kbir, Ta' Wied Għomor and Misraħ Lewża.

Although mostly agricultural, the area supports maquis communities, composed predominantly of carob trees (Ceratonia siliqua). Important species within this valley system include cage thistle (Atractylis cancellata), evergreen rose (Rosa sempervirens), Maltese spider orchid (Ophrys sphegodes subsp. melitensis), club-moss (Selaginella denticulata), Sicilian squill (Scilla sicula) and Mediterranean meadow brome (Bromus commutatus subsp. neglectus).

Mepa scheduled Wied il-Kbir and Wied Għomor as an Area of Ecological Importance and Site of Scientific Importance as per Government Notice No. 409/96 in the Government Gazette dated June 1, 1999.