The cervix makes EWCM. It is triggered by the same hormones that allow the ovary to release the egg.
The cervix is usually closed tight and plugged by a thick mucous that is hostile to sperm. Just prior to ovulation the cervix opens up and creates a more alkaline mucous that is nourishing to the sperm and allows it to pass through. You are at your most fertile when you have a thin, clear stretchy mucous.
Once your secretions have changed back to an opaque colour or sticky consistency then ovulation has passed. Usually within 24 hours of your peak symptoms.

Research the Billings Method if you need more details.

HTH