Jesse SWIM across, Does that sound right? NO! So cancel that word out of the selection and we are left with.. Jesse SWUM across and Jesse SWAM across. I would go with SWUM, because swam sounds more like a present kind of thing, and they are talking about last summer. So He SWUM.
1) it's dark
2) they are in the dark sky
3)there are stars in the dark sky that reflects in lakes and rivers
hope it helps!
The poet should not stray far from the meter. Or are you looking for another answer of what it should not include?