Based on your photo I suspect the majority of your muck is organic based due to the strong watershed slope on one side and very common plant growth around the edges. Eco-bio friendly bacterial digestors are typically slow acting when deep muck is present. For 2ft of muck be prepared for a long, frustrating costly, process. The bacterial products depending on brand and conditions may not do a lot more than keep up with the 2017 muck accumulation due to new organic growths and nutrient stimulated plants from the trout manure and the muck nutrient release. Keep in mind that bacterial products work best in warm water. As the temperatures increase above 60F and more toward 80F they work much faster. After several years of microbial additions you still may not be near your goal especially since your pond stays cool of 55F during summer.
Barley Straw. There are many species of algae that 'scoff' at the algae inhibiting chemical released by b.straw. Try it and see the effectiveness of it in your situation. When you use it, be sure to use a method that allows timely removal of the straw so it does not decompose and add to your muck problem.
There is a company near me in Ohio that uses a two man team of divers that use a trash pump suction system to remove-vacuum out pond muck. I have watched the process a few times. It is slightly cheaper and quicker than draining and dredging out sediments. Explore that option with divers in Colorado.
https://mucksuckers.com/In the end, after spending lots of dollars on eco-bio friendly products it may be cheaper and will definitely be a lot quicker to drain and have most of the muck dipped out. The ultimate cost could probably be about equal for both methods. Keep in mind you will also have algae plant issues to deal with during and from natural digestion of all the organic materials that will release plant growing nutrients each day during the year, not to count the new inputs. Nutrients will grow plants. It is what they do.
Your pond location is conducive to using a temporary siphon drain system to cost effectively remove the water so back hoe can dip out most of the muck from most or all of your pond. Once you get the pond drained down you may be able with a 3" trash pump, vacuum out most of the sloppy muck yourself with some help. As the pond fills to make the remaining muck sloppy and soupy repump it out. The process will be a dirty, wet, chilly procedure.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=462069#Post462069Your water flow input would soon refill the pond for long term enjoyment, less muck-weed frustration, improved aesthetics, and some deeper better water quality for growing fish.
