Blackberry - Rubus sp.

Woody shrub that produce only leaves in their first year of growth. They produce leaves, flowers, and berries in their second year in dense thickets. Blackberry canes have thorns. They produce white, 5-petaled flowers in spring. The berries, which ripen in mid to late summer, are aggregate fruits (many drupelets connected together with one seed inside each globule) that are purple-black and glossy when ripe.

I found a bunch of these shrubs growing on the edge of a lake.