In 1983, the State Pollution Control Commission undertook an investigation into the causes of poor water quality in the lake. The final report of this investigation, known as "The Environmental Audit of Lake Macquarie", identified the primary causes of concern, highlighting the major problems of sedimentation and nutrient enrichment. Accelerated sedimentation levels were estimated at per annum and nutrient levels had shown a substantial increase as a result of urbanisation. A study prepared for Lake Macquarie City Council in 1995 estimated that sediment loads to Lake Macquarie were per annum, which was very different from the sediment loads prior to European development, estimated at per annum. Two creek systems, Cockle and Dora Creeks, were estimated to be contributing and per annum respectively.