This spider is a member of the Nursery Web Spiders.
They are large spiders who are best known as Fishing Spiders for their tendency to hunt on and under water.
They are semi-aquatic and can actually stay underwater for thirty minutes. They feed on aquatic insects and small fish.
The females produce large egg sacs which they carry in their jaws. She does not feed until the spiderlings emerge.

I discovered this female after finding her egg sac and spiderlings in a nursery web that she had created in the leaves of a weed along the trail.
She was perched a few inches above the spiderlings.
They have shockingly large leg spans and are quite impressive spiders. The female of this species can have a body length of 17 to 24 mm and a leg span of 55 to 80 mm.

Spring Valley County Park
York County
Pennsylvania