Pond Solar Heating?

Ok I know that "Spring has sprung" and all - but my pond does get a lot
of shade and warms up slow.
I have wondered about the idea of a using solar heat from a roof top
collector to warm the pond to a better temp and extend the active season
for my finned friends. Not that I have actually done more than
thinking about it - living is coastal BC is about the worst place next
to Washington state for hours of sun shine anyway. But I thought if
nothing else maybe it would be an interesting thought experiment and who
knows maybe someone out there has tried it. I am thinking that one
would need a water/water heat exchanger because circulating pond water
up through a collector would grow algae and clog I am sure.
Crazy idea? what do people think?

Cheers.