We're about 100 ft from a stream and uphill of it. As for soil, it
seems very orgainic, hold water very well, and weeds love it.

Wouldn't rolling the yard really compress and damage the grass roots?

the grass root is not that delicate. the grass roots can go several inches below
the soil surface. the wide surface area of the roller is not narrow enough to
ruin the soil surface area and harm the grass roots.