Question: do you have a fine droplet sprinkler near these plants?

Yes, unfortunately in our sandy soil, which is pretty much the consistency of a kid's sandbox, that is the only way to get everything well watered. The drip line just waters straight down and doesn't spread.

I have a micro-sprinkler that sprays a very fine mist of water.

The lesions confined by the veins look like angular leaf spot caused by the bacteria Pseudomonas syringae. It's pretty common on cucumbers.

It survives on plant debris so sanitation is a big part of control. It also hangs out in the soil, so rotating out to something less susceptible for a few years would help. If re-planting with cucumbers, it's best to use pathogen free seeds if you can. I'm not really sure how that works in a home owner situation. There are also resistant varieties available.

Unfortunately, there isn't any way to get rid of it now that you have it. You can slow the spread by watering early in the morning to allow the leaves to dry more quickly. Also, only pick fruit when the plants are dry.