Can I use GPS without Navionics Card?

Hi all -

Bought a Pro 7 with Nav+, promptly lost the Nav+ card.

With the GPS feature, can I still use the chartplotter, and will it show me any detail on the US lakes? It seemed like it was not giving me any water detail when I was out on Bull Shoals Lake, and the water appeared the same way land does.

Appreciate any help/advice.