How deep can you reach and still keep your face above water? Use that as
your guide to depth. Unless you fancy having a pond water facial.

What are you reaching for? A long pole net can rescue dropped items.
Repotting lilies... maybe have nylon ropes attached so they can be
'fished' out? Or just snorkle once a decade...

I don't have marginal plants. Anacharis manages itself.

Heck, around here I could advertise and SELL pond facials :-)