If I primarily fish cedar creek lake, Do I need to invest in a nav chip for my unit?

Well for the best detail i would say yet. all you can do it see if the stock maps have one-foot increments.

Thank you

I tried to post pictures, but this place is horrible to post pics on. I sent you a pm with my phone number.

You see can Cedar Creek here

https://webapp.navionics.com/#boating@6&key=ceoaEphboQ

Finally figured it out.

Yes, the Navionics Platinum South or the Nav+ Regions south would be your best bet for that lake and that chart plotter. As mentioned above, you can check out the detail and mapping available for free on the Webapp before you spend a dime, that way you can decide if it is right for you, before dropping any money.