Section R. 323.1069 - Temperature; general considerationsRule 69.
(1) In all surface waters of the state, the points of temperature measurement normally shall be in the surface 1 meter; however, where turbulence, sinking plumes, discharge inertia or other phenomena upset the natural thermal distribution patterns of receiving waters, temperature measurements shall be required to identify the spatial characteristics of the thermal profile.(2) Monthly maximum temperatures, based on the ninetieth percentile occurrence of natural water temperatures plus the increase allowed at the edge of the mixing zone and in part on long-term physiological needs of fish, may be exceeded for short periods when natural water temperatures exceed the ninetieth percentile occurrence. Temperature increases during these periods may be permitted by the department, but in all cases shall not be greater than the natural water temperature plus the increase allowed at the edge of the mixing zone.(3) Natural daily and seasonal temperature fluctuations of the receivingwaters shall be preserved.Mich. Admin. Code R. 323.1069