Field studies have shown that growth of Sphaerotilus is triggered into nuisance concentrations during certain seasons of the year between Camas and Longview in the Columbia River and between Oregon City and Upper Portland Harbor in the Lower Willamette River. Floods and freshets influence the growth. At such times growths are loosened en masse and transported many miles to points downstream. Moreover, high water and floods shorten time of flow to downstream points so that transportation of nutrients occurs over much longer distances and the range of active slime growth is extended accordingly. The sulfite pulp mills were found a major contributor to the production of Sphaerotilus and associated slimes in the Columbia River. Kraft mills, canneries and domestic sewage are other lesser contributors.