Mercury nitrate was discharged to the river by the hatting industry from circa 1860 through the first half of the 1900s. The hat factories used the chemical in the felt making process to remove animal fur from pelts. During this time, levels of mercury were found to be 5-10 ppm with extremes up to 100 ppm. These levels were about 500 times higher than background levels. Although the hatting industry was the main cause of mercury pollution, there were other industries that contributed as well. The P. Robinson Fur Cutting Company was a fur removal company sited on the Still River.