Guys, I'm still in the beginning phases of a lake resurrection from 40 years ago. If I know that the lake held water for 20 years, is there a need to do soil tests / test holes? Also- is there a need to remove layers of top soil that have accumulated over the last 40 years?

Seems like as long as I invest my research, time, and quality into a leak free dam, that the (2) creek fed lakebed would sort itself out, even if the bottom was porous in some areas?