The graph below shows the salmon population, in thousands of pounds, in the Columbia River, from 1866 to 1983. The graph below shows the salmon population, in thousands of pounds, in the Columbia River, from 1866 to 1983. Salmon populations increase between 1866 and 1879, then fluctuate at a steady rate between 1879 and 1931. From 1931-1983, the salmon population steadily decreases. Based on the graph, which of these conclusions is most likely correct? Question options: A large amount of contaminants were present in the river between 1910 and 1912. A series of large hydropower units were built on the river after 1931. The salmon did not breed between 1866 and 1879. The hydropower units on the river were deactivated after 1970.