Without photo- hard to say. My cukes have a similar look and I am assuming it is slugs or snails...Try putting out a beer dish and see what you catch. Last year I picked snails off my pumpkins by the dozens. Check out your plants in the early morning and see if anything is munching....
That looks like it. Though reading the description I have no clue how it got here. I bought seeds from a reputable source, we use our own water, the garden is in a new place then from where the previous owners had theirs 5+ years ago.