Certified Advanced & Nitrox diver here (w/ some other specialties). Hubby's a PADI Course Director, top level instructor of instructors, DAN instructor trainer, dry suit, advanced nitrox/enriched air instructor trainer, rescue diver and a bazillion other certs/specs. In fact, for fun, he went diving in the Arctic a few years ago. Water temp was 29 degrees, as salinity lowers freezing temp. It's his goal to take one of the dive trips offered to the Antartic.
High altitude, cold water, depth, air mix, and bottom terrain will all impact the search. Months ago when we were discussing this/ it was in the media, it was reported they were diving in 40 ft, using trimix, and could only be in the water 20-30 min 1/day. With that info, both hubby and I called BS, as they could've done two twenty minute dives per day under those conditions, in dry suits/cold water regs/equipment, and trimix would've been an unnecessary expense. Recently, I looked up the res info, and it looks like it's up to 121 ft deep, which would be calculated even deeper than that on dive tables due to altitude. If they were diving to that depth, the trimix and time restraints make more sense.
The cold and high altitude diving aren't unusual circumstances for many colorado divers. The altitude and depth is what restricts bottom time, and the cold can be numbing even through the right gear, so it's harder to feel things, if you're forced to search tactilely due to low vis/low light. (Tactile portion from article I read some time ago re: recovery diving.) IMO, what'd be hardest is that you can't stay down long and search, so it's time consuming (read cost), may require enriched air depending on depth (cost), and a lake bottom can be filled with debris, trees, boulders, which are hazards and obstructions. It's expensive and hard, but IMO, they need an experienced, tenacious, high altitude, cold water, recovery diving team.
It can be done. As stated in quoted post, it's been done before. I tried to snip a bunch of potential resources for the fam to look into last night that could help.
Moo