Cody Note. esshup is very correct for overall thermal tolerance of water temperature for trout (70F). However a 20 to 25 ft deep northern mid michigan pond without bottom aeration will be significantly thermally stratified in summer when the surface is 72+F. Thermocline in 2-3 ac depending on wind fetch could be at 7-8ft. Water temperature below the thermocline at 8 to 24ft deep could easily range from 65F to 60F. However the DO could be 0 to 8ppm depending on water clarity. The less the Secchi disk reading the closer the DO will be to 0. This is why for growing trout in a northern pond one should have a secchi disk and a thermometer with a cable or probe to measure the pond water temperature profile. A DO / temperature meter is best for this measurement.
If it were my pond for a potential trout fishery, I would spend the money to make the overall pond deeper toward 25ft maybe some water 30 ft deep and smaller size instead of building a larger pond of toward 3 ac. Keep the side slopes steep and minimize the amount of shallow water that promotes abundant submerged vegetation. Shallow water and abundant dead weeds consume lots of dissolved oxygen at all depths. Encourage good marginal shoreline plants and submerged vegetation such as longleaf (American) pondweed or broadleaf pondweed (Potomogeton amplifolius); maybe some eel grass or elodea a more cool water plant.
Beneficial Pond Plants Forum topic
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=440475#Post440475
