Lake Claremont lies in a depression in the Spearwood System of coastal sand dunes. It is a true swamp geographically, that is it is the above ground part of the massive underground water system common to most parts of the Perth coastal plain (Morris and Knott, 1979,145). This subsoil water flows continuously towards the river and ocean in a north east to south west direction.
The swamp lies in a valley between coastal dunes where the ground rises rapidly from 1.5 metres to 12 metres. Immediately prior to 1950, the swamp at high water mark enclosed an area of approximately 20 hectares. During the 1950s and 1960s areas were reclaimed and this reduced the area of the open water to approximately 15.7 hectares at high water mark (Emory, 1975, 35). At the north east and southern end of the swamp are two valleys and it has been hypothesised that these valleys may have been scoured out by river action (Evans and Sherlock, 1950, 152). Apart from these two openings, the area consists of coastal sand dunes of aeolian origin, partly consolidated by low shrub vegetation and intermittent wattle (Evans and Sherlock, 1950, 151).
The soil of the coastal plain near Claremont is a fine graded silica and calcium carbonate sand. Water action on the carbonate has in places cemented the sand into sandstone mass calcific sheets and pinnacles. In the actual vicinity of the swamp there is a thin deposit of marl, consisting of detrital material settling out of solution from swamp waters (Evans and Sherlock, 1950, 152). Spearwood sands generally have a relatively high iron content in comparison to other sandy soils of the Swan coastal plain. As a result they have the capacity to initially adsorb phosphates leached from fertilisers and septic disposal systems. However, in the longer term the phosphate adsorption capacity saturates and nutrients are readily leachable to the ground water, drains or lake.
References
Emory, K. et al. (1975) ‘Waterfowl seen at Lake Claremont (Butler's Swamp) in the Spring of 1972 and 1974’, W.A. Naturalist 2, p.7.
Evans, G.A. & Sherlock, N.A. (1950) ‘Butlers Swamp, Claremont’, W.A. Naturalist 2, p.7.
Morris , K.D. & Knott, B. (1979) ‘Waterfowl Utilisation of Lake Claremont During 1977’, W.A. Naturalist 14, p.6.