I live at Lee-on-Solent. There are a few sails out there now but not too many. I rang around the local marinas and stopping points yesterday and although they are all letting local boats out to play they are not accepting visitors on the basis that government guidelines still say you need to return to your own bed each evening. The guys who are out there are therefore returning home each day or hiding in an anchorage overnight.
The hamble was really clear during lockdown. I went down on the Wednesday evening after lockdown was removed and the clarity was about 3-4 feet. It is not now.
Oh right! You meant literally "water clear" ..... Well two things. The bottom is stirred up by heavy weather and high traffic. We have had neither recently. Having lived here since 1984 I can tell you that the weather has more of an effect on clarity of the water near the Lee shore than boats do. Obviously rivers like the Hamble will be different.