Oldfield River

Seven sites were sampled on the Oldfield River system and are shown on the map above. Photographs are available for each site:



The Oldfield river was sampled for this project between 29th August and the 11th September 2006. At this time the following water quality, river foreshore condition, fish and macroinvertebrates were recorded.


A high variation of 32 different types of macroinvertebrates was found at site OLD04 with many freshwater opportunistic species reflecting the low salinity, including tadpoles. The lowest number of macroinvertebrates were found at site OLD05.

Two types of Amphipoda were found in the river that are of particular interest as they are new species that have not been described.

Pictures of these can be seen in the gallery.


Four fish types were found in the river and these were Hardyhead, Black bream, Goby and Spotted Minnow. Pictures of these can be seen in the gallery.

River foreshore vegetation condition

The vegetation condition next to the sites varied from pristine at the upper sites to degraded at the lower sites.

Sites OLD07 - OLD05 were considered pristine with the river embankments and floodway entirely vegetated with native plant species and no evidence of human or livestock damage. Sites OLD004 and OLD03 were slightly disturbed with some areas of human disturbance and weeds. The two lowest sites OLD02 and OLD01 were considered degraded and weed infested with greater weed infestation at the lowest site.

Water Quality

Water samples were only taken once from each site so while they help describe the water quality at the time the results can not be used to explain the state of the river for the rest of the time.

While the river is naturally saline, the salinity varied greatly along its length. The upmost pool (OLD07) was the saltiest with 87.2 ppt (parts per thousand) which is over twice as salty as seawater (35 ppt) and hypersaline, this pool was small where evaporation would be significant. The lowest salinity was recorded in OLD04 with only 2 ppt which was muddy fresh water in Cheadanup Creek. OLD06 had considerably lower salinity (9.7 ppt) then the pools both upstream and downstream. This may be due in part to the large size of the pool and as such lower evaporation rates.

Nutrients samples indicated that high nitrogen levels were recorded at sites OLD01, 02, 04 and 07. Phosphorus levels were generally lower with the exception of sites OLD02 and 07. The upmost site OLD07 had the highest phosphorus and nitrogen levels for the river which is surprising given its situation in pristine wilderness. One possible explanation is the contribution of nutrients following the severe fires around the site in 2003 which would have resulted in large amounts of ash and sediment being washed into the pool bringing nutrients.

High chlorophyll levels were recorded in the lower sites, particularly OLD02 which had quite high nutrient levels. The chlorophyll indicate high levels of microcellular phytoplankton growth.