Algae bloom. It is likely that the pH is way off.
Add shock and liquid chlorine to kill it (it will take a lot)., circulate the water while this is done.
Once the algae is killed off, clean the pool, and then clean the pool filter (recharge with DE if it's a DE filter).
Use a pH test kit to determine the pH, then add acid if the pH is too high, or pH Up if the pH is too low.
Once the pH is correct, add some algaecide to suppress any subsequent growth, and maintain a good level of chlorine..
- chemist and pool owner
Dito @ Doctorwho's words of advice..('cause they are true words of advice!)
Water light green and cloudy
