Algae comes in various forms. So you can get
green water (free floating green cells) and stringy
algae on the side, floating clumps, fuzzy algae
that covers everything.
Some algae is good, natural to the pond. Too much
yukky algae and the pond is out of balance.
Biggest culprits - too many fish, overfeeding the fish
and accumulated gunk.
All algae thrives on sun, fresh water, fish waste, plant waste,
blown in dirt.
Letting the frogbit expand will help provide shade
and compete for the nutrients that algae likes.
Plants are always a good idea.
Fewer fish helps, getting out gunk, shade.

Lots of folks run their water thru a separate tank
filled with plants to suck up all those nutrients
(we call it a veggie filter).

Most of us run our fountains and waterfalls 24/7.
Nighttime is when the fish can be stressed for
oxygen as the plants use o2 at night and switch
during the day. A good indication your fish are
out of o2 is to view the pond just before sunrise.
If they are gasping at the surface they need water
movement at night. An airstone attached to an
air pump will help too.

Some ponds use ultra violet light to kill algae
cells. It is set into a line that runs to a mechanical
or biological filter.

One thing I don't recommend is algaecides as they
make suddenly dead algae which stresses the pond
and provides tasty dead plant material for new
algae to consume.

Am also in PNW, SE WA.
k :-)