I have made this bass fishing cake design before, just not this big and not one that needed to include chocolate buttercream.
See Hollie had some of my yummy Hershey's chocolate buttercream icing on another cake and HAD to have more! So I came up with a two tiered cake that would allow for a "muddy bottom lake" effect! The whole bottom layer is iced in chocolate buttercream and I brought the water down on top of that for the wavy water effect.
What a wonderful and momentous birthday to celebrate! 80 years is an amazing life! "PaPa" must be an avid fisherman, so we gave him one he could eat....wait....you CAN eat fish.....okay, one you can eat that tastes SWEET! Hee Hee!
The fish is actually molded from Rice Krispie Treats and covered in fondant/modeling chocolate and hand painted with food color paste. The "water splash" is made from modeling chocolate made the same color as the buttercream icing.

I put a fish hook with a worm and then made the fishing line spell out the birthday message to PaPa!

(See the fish's tail sticking out at the bottom of the top tier?....you gotta love it!)
Here is the complete design. With buttercream and fondant accents and chocolate rocks!

Congratulations on 80 years of life and here's to many more to come!