That looks like some variation of zucchini to me. You could tell for sure when it does flower.

Probably WATERMELON. If it grows vine , it will be a confirmation.

Looks more like zucchini to me.

I vote for watermelon

I showed this to my wife. She immediately said watermelon.

My opinion? If the leaves are smooth I go with watermelon. If the leaves have fine hairs, then I go with zucchini.

OR -- it could be from compost (especially since it sounds like you didn't plant it), in which case it could be a mix that looks like watermelon and tastes like zucchini. :)
I say grow it out and see.

It's watermelon.....positively

Watermelon and zuke can't cross -- two different species. That's a watermelon.

OK, so you can't pull it, you have to leave it now and report back!

Looks like a watermelon to me as well.

Rodney

Looks like my watermelon.

BTW: watermelon and zucchini wont cross. So it is either WM( I said before) or (Unlikely, imo) a zucchini..

Watermelon has a unique leave shape and color among the big cucurbits family.

Thanks, I don't know how it ended up here, but my husband and I are exited to have a watermelon growing organically in our yard . Thanks again for all your help