Looks like foamy eye - an infection.
If you make or buy a mild saline solution (there's a recipe on WebMD) and gently spray or drip saline solution into the eye 4 or 5 times a day, that may knock it out. If it has gotten more of a hold, you may need to go to medicated eye drops or gel.
I would also add a tablespoon of apple cider vinegar per gallon of drinking/head washing water to help knock out some of the bacteria.