Intelligent Knowledge Based Systems are computer programs which exhibit machine intelligence. Machine intelligence is the capability of a computer to efficiently search through large quantities of heuristics (rules of thumb), and expert and domain knowledge in order to achieve inferential conclusions. WatQUAS 2.0 is an Intelligent Knowledge Based System (Expert System) for the assessment of water quality of Ontario rivers. WatQUAS 2.0 operates on an IBM PC compatible computer and is highly user interactive. A Data Base Management System is utilized to organize and contain large quantities of historical water quality data, parameter and site specific knowledge. WatQUAS 2.0 contains knowledge pertaining to approximately 255 water quality contaminants. The Expert System component of WatQUAS 2.0 examines various water quality problems and situations and achieves inferential interpretations and conclusions. The water quality assessment techniques employed by WatQUAS 2.0 have been expanded and enhanced from the prototype version. Future work involves completing the computer programming of the Expert System, expanding the knowledge base and programming WatQUAS to examine more water quality assessment areas. Comprehensive testing and evaluation is also required.