The effect of bird density on water quality parameters of Collins Lake was examined at three time scales: yearly, seasonally, and weekly. There was no relationship between bird sightings and either coliform bacteria or Secchi disc transparency on a seasonal or long-term (19 year) period. There was also no increase in spring chlorophyll levels over the 19 year period, even though the annual total bird sightings increased almost three times over that period. However, chlorophyll levels did increase during the ice-free season as shown by an almost doubling of fall chlorophyll levels between 1978 and 1997. Increased bird density is considered the most probable cause for these elevated fall chlorophyll levels. The increase in summer resident birds appeared to have a greater effect on chlorophyll levels than migratory birds. There was no observable effect of bird density on chlorophyll levels on a weekly basis, but the large number of other variables changing in the lake during the study period may obscure any trend on this time scale.