As a Department of Environmental Protection officer reminded me on day, "The friend of pollution is dilution." I would hope they have a filtration system in place that will screen out the plastics and other non-biodegradables, so I am sure in the long run this will have no discernible impact on the river. However, the precedents that it sets is troubling. If one city can do it, why not several smaller towns, after all, it is a cheaper alternative for reclaiming wastes. But if everyone does it, then it becomes too much to dilute, and we have a situation.
So, the immediate idea, although it makes the skin crawl, is not really a hazard to the river, estuary, or the wildlife. It is the psychological damage, and the precedents it sets that is the real issue. Maybe a more costly track should have been taken ...