Green water is green because of the algae growing in it.
Algae needs light to survive.
Solution = cover the pond to exclude the light, and all the algae will die.
Result = clear water.
Job done.

The reason why the pond is full of algae is because there are too many nutrients in it. Probably leaves have blown in or as was the case with my pond this year some frogs died after being frozen in in December.

Covering the pond will kill the algae but as soon as it is uncovered they'll grow again.

You need to have at least half of the ponds surface covered with plants such as water lillies.

Alternatively there are algae killing chemicals you can add but I've never used them myself

Pea soup ponds are common in the spring, anyway. Around here we usually just wait a few weeks, and the problem goes away by itself, as the pond ecology re-balances. If it persists after a couple of weeks of "creative loafing", then is the time to start taking action: waterlilies for shading, submerged and bog plants to soak up excess nitrogen, etc.