Culham Inlet is fed by two rivers, with a combined catchment area of 2307 square kilometres, and unnamed drainage from the Eyre range. The Steere River originates 25 kilometres north of the inlet and the Phillips River has its headwaters 120 kilometres inland. The major tributary of the Phillips River is the West River. These rivers are typical of those in the area as they normally have low flow, are naturally saline and experience unpredictable and sporadic flooding.

The Steere River originates in the Ravensthorpe Range in the vicinity of Elverdton and in a subdued stony plateau west of Elverdton. As such it is one of the shortest south coast rivers with a main channel length of 30 kilometres and a catchment area of 36 000 hectares of which 30% has been cleared for agriculture. All the upper catchment is uncleared bushland, a very small proportion of which has been severely impacted by mining activity. The median annual rainfall in the catchment is 450 mm and the mean annual flow estimate is 1,400 ML. (This information is from Andy Chapman's Steere River Condition Assessment, 2007).

The Phillips, West and Steere rivers were sampled on the 3rd to 5th of October 2006 and the 7th of September 2007.

Three different types of fish were found, the Gobi, Spotted Minnow and Hardy head, shrimps were also found. Pictures of these species can be viewed in the gallery. Some tadpoles were found in Carracarra Creek (PHI02).

The vegetation condition next to the sites varied from near pristine to degraded. Generally the sites surrounded by vegetated reserves were in better condition, at these sites there were often a few weeds but the vegetation was healthy and predominantly native. Site WES02 where the West River crosses the South Coast Highway the vegetation was in the most degraded condition with weeds as the dominant understorey.

Vegetation surveys along each of the rivers suggest that the vegetation corridors along the rivers form an important link from the coast to the inland areas. In the case of the Phillips and West rivers, the foreshore vegetation is generally in very good condition with most fenced off from adjacent farmland. A recent assessment of the Steere River and its tributaries found that weed infestation was degrading the main river channel and that the tributaries showed additional manifestations of degradation including erosion, excess sediment transport, secondary salinisation and water impoundment.

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

The water temperature at the time of sampling ranged from 13 to 21.5°C.

Salinity was very low (3.45ppt) in the pool on Carracarrup Creek (site PHI02) where the tadpoles were found. The remainder of the sites on the Phillips River had high salinities from 32ppt up to 69ppt which is well over seawater at 35ppt. The West River had salinities decreasing from 72ppt at the most upstream site on the river to only 12ppt at the lowest site where the West River is in the national park. The site of the Steere River (STE01) had a low salinity (9.8 ppt) compared to the other two rivers.

The water measured ranged in acidity from pH 6.58 to pH 8.83 which is close to neutral (pH 7) to slightly basic.

Nutrient levels were greatest for both nitrogen and phosphorus at site WES03 which is higher up in the West River catchment. The Steere and lower West River sites had the lowest levels at 7-8 µg/L phosphorus and 730 µg/L nitrogen. The West River had reducing nutrient levels as the sites went downstream but for the Phillips River nutrient concentrations remained high with the lowest site, which is connected to the inlet, had 75 µg/L phosphorus and 3000 µg/L nitrogen.