Here is the project summary:
The watershed tributary Golf Course Creek (GCC) added 1065 kilograms of Nitrogen (analyzed as TN) and 120 kilograms of Phosphorus (analyzed as TP) nutrients to Sylvan Lake in the April-September period of 2014. Total Nitrogen and Total Phosphorus compositions of water quality samples and the measured cumulative flow in the GCC stream were used to calculate lake loading by those nutrients. Flow in GCC was found to be about 12 percent of precipitation incident on the 26.3 square kilometre catchment area after the month of April when snow melt runoff had ceased. Because of mixing of the cumulative GCC flow of about 1.4 million cubic metres of water in the lake volume of 420 million cubic metres, the TP load from GCC increased the equivalent concentration in the lake by about 1.4%.
Click on this hyperlink for the final project report that is available for download.
Tributaries carry stuff from the land into the lake, according to the Second Law of the Watershed. They are important for the future health of the lake, and are targets for water quality control.
See this post for an explanation of the Two Laws of the Watershed.