Baby's Ears Submerged in Bath?

Can anyone tell me if it's ok if my baby's ears get submerged in bath water for a short amount of time in the bath??

We don't have a baby tub so what we usually do is fill our tub and I get in with our daughter and bathe her that way. Lately though she's been wanting to lay back and "float" or "swim" on her own but seems frustrated that I won't let her put her head farther back.

So I was thinking of just putting a few inches of water in the tub and just laying her on her back in it (I'd still be in there with her and she can't roll from back to belly yet). I'm just concerned about if it's ok if her ears get submerged for a short amount of time?