Sure, but if it’s only 40 days, wouldn’t some of the trees survive? And we have no idea about how much was “just mud”, although that’s not the indication in the Bible. As someone mentioned, the olive branch....
There was still a lot of water when the dove brought back the olive branch. The Bible, as usual, terse and short on details but one must assess that the olive branch probably came from a higher elevation. As for the mud, there’s no question about that. There was a great deal of mud everywhere. I’ve seen moderate flooding and there’s mud everywhere and it’s often very thick.