answer one. yes. you need to ...

answer one. yes. you need to put in a weir. it can be as simple as sand bags wrapped in geo membranes. or you can use containment nets. answer 2. you need to know what you are treating for. what is the issue? is it an oil spill or a chemical spill? is it fish kill? is it cyano toxins and cyano bacteria? is it heavy metals? is it stinky and its a dead zone? once you have determined that, you can then easily come up with a solutions. one rule though is to not add more load to the river. not to add more chemicals or pollutants to the river. a river should have no smell, no sludge, and is very supportive to life. highly oxygenated is best. cost is a big issue and thus if the ecosystem is restored, it can be sustainable.