I have found that on lakes that get more use, the maps are pretty good. They came out and used a sounder to map out the lake bottom terrain with detail. Boysen, the Gorge, Lake Powell are all decent. I guess it is not worth it for them to survey the less popular lakes (like Fremont, and all the big lakes around Pinedale). Those maps are useless, show no detail at all.
As Appleye stated, check the current lake level and adjust it on the app to get the most accurate map....