I really have no experience in draining and cleaning out the muck. I have looked into different outfits but they all are asking 40k+ to do this kind of operation. Could you point to any resources about how to go about doing this?
There are some missing pieces but if you would fill those in I could offer some suggestions. First, is a dam constructed or is this a natural pool in a stream bed? What are the dimensions? What is the gradient of stream? Does the stream have a clay or stone bottom? Is the source of flow from many very small springs upstream or is there a strong spring supplying the stream very close by? Does the flow get very large in rain events? I get the impression that this lies in a forested area and the muck is sourced to terrestrial leaf inputs. Also any additional information that these questions make you think of, add that too.