In this work we took three samples from the flowing Tigris River in Salahuddin - Iraq. Through this research was obtained two benefits, first determine the amount of attenuation by a helium neon laser, and the second measurement of the concentration of plankton in the flowing Tigris River by the measured unit mass regions. Results showed that the. Al-fat ha sample that was tested based on this scheme has been found that the amount of micro plankton river which is equal to (0.5) gm per (500) ml when the permeative intensity is equal to (32) lux. m² and this is shown in figure (4), while in figure (5) appeared the proportion of river micro plankton in Tikrit sample (0.59) gm per (500) ml when the permeative intensity (29) lux.m2 and this difference in intensity between the two samples is due to logical reasons, The first reason is due to the location of each of the two samples, since Al-fat,ha is located in the northern city of Tikrit, is higher than the city of Tikrit above sea level, so the arable land remnants besides micro plankton river drift toward the city of Tikrit, and the second reason is the remnants of human population of Tikrit city.