Hehe... sounds like diving in a bloom here in the warmer months. sometimes the layer of algae is 10 metres deep and though the water is crystal underneath, it is so dark down there... really creepy... I love it.
It can be really disorientating tho... when you judge your speed wrong and the bottom never seems to appear or comes rushing up at you out of nowhere.
Worst it ever got there was only a couple of feet of clear water on the bottom and I went face first into millions of ugly brittlestars and sediment... then bolted for the surface, heart racing
You can keep track of the surface with your chin tucked in, if it is sunny enough up there but you need to keep a hand in front of your head incase you bang yourself out on a rock or something... I almost impaled myself on a big pointy anchor so not always too clever.
I've never tried it but I reckon ff you wanna look where you are going or you can't track the surface then you could prolly keep something bouyant on you to show you which way is up... little float keyring trinket or something... and don't get scared now
