"In the 1960s I worked as an aquatic biologist on the lower Mississippi River and one of the most interesting assignments I had when I worked on the Mississippi was to survey pool 2 of the river. This is the stretch of river that runs from the Ford dam down to the Hastings dam and it's the area that is immediately below the Twin Cities, so it's an area that was very badly polluted in 1964. At that time there was one sewage treatment plant for the Twin Cities at Pigs Eye and it was badly overloaded, plus the Minnesota River had a very heavy load of sediment and a lot of untreated waste from the communities at the lower end. So pool 2 of the river was overloaded with organic waste and with silt.
"About 1964 we realized that something had to be done about the river and there was talk about upgrading the sewage treatment facility at Pigs Eye. I was asked to do a survey of the fish population to document the condition of the fish population and to gather information that would be useful for upgrading the water quality standards for the pool.
"At that time it was real common for the oxygen in the river to be zero during the middle of the summer and also to be zero in the middle of winter. This would be times of the year generally when flows were low, so there really wasn't enough flow in the river to adequately dilute the waste from the Twin Cities and from the Minnesota River. So, needless to say, an oxygen level of zero is very, very low. Fish can't survive at that concentration for very long, and in fact a warm water fish population requires an average of about 5 ppm of oxygen.
"So the river was badly overloaded with waste, which reduced the oxygen. In a situation like that the biota respond. The fish species that are the most tolerant of low oxygen will become very abundant; the game species that generally require higher oxygen levels will decline. And in fact the fish population takes on a real poor structure dominated by what we would call rough fish. So, in '64 we started surveying at the lower end of the pool and we worked upstream and basically, what we found was a fish population dominated by carp, by black bullheads and by species that could tolerate low oxygen.
"And in fact we got to a point as we moved upstream where there were no fish at all. In general about the area of Grey Cloud Island we start getting what we call waterhauls where we would set our test nets and come back the next day to see what we caught to measure and weigh the fish and there were no fish at all. Another symptom or another sign of really bad conditions out there was that when we did catch fish in our nets they would be dead and bloated. This is because in order for fish to survive they had to keep moving, if they were confined in the net overnight, the oxygen dropped and they died. Another indication of bad conditions was the fish themselves. They had a real bad condition factor. The fish were extremely thin, they were soft-fleshed, and in fact just from being in the net, the noses would rub off some of the fish species like the carp; I had never seen that before.
"In general, conditions in the river were extreme on the bottom as well. The oxygen was very low in the water column. But there were huge areas of organic black ooze covered by sewage fungus. In fact I recall one experience where we moved into the shallows to set our test net and I thought I was looking at the bottom of the river when in fact I was looking at the top of a bit of this organic ooze. I dropped the net into the river and it sunk into about 3 feet of this black, tarry substance. We had to pull the net back into the boat, and I'll never forget that experience. We literally became covered by this black ooze, the inside of the boat, all of our clothes, ourselves-it was a real mess. There were also large areas where there were decomposition gases coming off the bottom; things like ammonia, things like methane, hydrogen sulfide-and this was all because of the overloading of organic material.
"As we moved up the pool and got actually above the sewage treatment plant, the oxygen levels returned to more normal levels. The Minnesota River actually enters the pool upstream of the sewage treatment plant, so there was some depression of oxygen but it wasnÕt quite as bad as it was in the lower end of the pool. Here perhaps the most prevalent problem in addition to the inflow of the Minnesota River was the impact of combined flows. By combined flow I mean an inflow where a storm sewer is connected to a sanitary sewer. There was actually raw sewage coming out of the storm sewers back in 1964. And in fact, a couple of locations where we had nets set downstream of where these large storm sewers entered the river, and coming back the next day to pick up our nets they were almost impossible to lift because they were totally entwined with toilet paper, sewage debris, and it was just an unbelievable mess.
"That part of the survey wasn't much fun. So the combined flows were a real problem in addition to the amount of sediment that was coming out of the Minnesota River. Once we got out above the mouth of the Minnesota River and got into cleaner water you could immediately see how the fish pop responded. It took on a much better structure and you started seeing clean water species. Smallmouth bass is a good example. All of a sudden, smallmouth bass were in the river. This was because that stretch of river didn't have the severe overloading and didn't have the depression of oxygen. So in the upper end of the pool, the fish population took on a much more normal structure which would be similar to an unpolluted river. So, it's a real outstanding example as to how wastes impact water quality and how water quality impacts the condition of the biota, or the condition of the fish population."