W Dale wrote:

I have heard that your fish and sunken plants still need sunlight. As
long as you do not completely cover the surface of the pond ...

They get perilously little sunlight in an ice- and snow-covered Ontario
pond, whether it's covered or not, so I'd say no.

Generally, tropical plants need sunlight year-round. Some will pull through
as house plants, some can't even get enough light that way in most houses.
Temperate plants usually expect a dormant period, and whether they get
little or no light makes no difference to them once they've shed their
leaves. Lilies put out tiny little indicator leaves that trigger growth
when the amount of sunlight picks up.
--
derek