A show-stopping cake with jelly “ocean”, swimming fish, and a sandy hill your kids can decorate!
This cake is pure birthday magic — layers of wobbly blue jelly filled with fondant koi fish, a sandy beach cake perched on top, and loads of lollies, umbrellas and fondant sea creatures. It looks impressive but is totally doable, especially if you spread the steps over a couple of days.
Perfect for summer birthdays, pool parties or beach-themed celebrations!
What You’ll Need
For the Jelly Aquarium (bottom layer):
- A large round plastic cake stand from Kmart (the tall clear one)
- 4–6 packets of blue jelly crystals
- Fondant (to make koi fish, turtles & seashells). Here is the mould we used.
- Optional: extra lollies like gummy rings, Sour Strips, and jelly babies (these look amazing “floating” in the layers)
For the Beach Cake (top layer):
- 1 round cake (any flavour)
- Buttercream icing
- Crushed biscuits or ground-up fondant (for sand)
- Mini cocktail umbrellas, you can shop here.
- Rainbow Sour Strips (for beach towels)
- Gummy bears or jelly babies
- M&Ms, extra lollies… fondant shapes. See more moulds here.
STEP 1: Make Your Fondant Sea Creatures
(Optional but so cute!)
Use fondant moulds to make:
- Koi fish
- Sea turtles
- Shells
Dust with edible glitter and let them air-dry.
Tip: Fondant will soften slightly in jelly — it’s fine! It just gives a more underwater look. Shop some moulds below.
STEP 2: Build the Jelly Aquarium Layer-by-Layer
This part takes time, but the result is so worth it.
- Mix your first batch of blue jelly and pour a shallow layer into the plastic cake stand.
- Let it set in the fridge.
- Place a few fish, turtles or lollies on the surface of the set layer.
- Mix and cool your next batch of jelly, then pour gently over the top.
- Repeat until your container is filled with “fish swimming at different depths”.
Tips:
Cool jelly slightly before pouring so it doesn’t melt earlier layers.
You can use gummy rings with lolly people to make cute “floaties”.
Add rainbow Sour Strips upright inside the jelly for colourful coral!
Refrigerate overnight for a firm base.
STEP 3: Make the Beach Hill
- Bake (or buy!) a round cake.
- Carve it into a sloping hill — think of a sand dune rising from the water.
- Cover the whole cake in buttercream.
- Grind up biscuits into fine “sand” and press it all over the icing.
- Place the sand hill on top of your jelly aquarium.
STEP 4: Decorate the Beach!
This is the fun part — and perfect for kids to join in.
Add:
- Mini cocktail umbrellas for shade
- Sour Strips as beach towels
- Jelly babies “sunbathing”
- M&Ms as colourful beach toys
- Fondant turtles crawling up the sand
- Extra shells, buckets and fish
Let your child claim their own section to decorate — it makes the finished cake even more special.
STEP 5: Serve & Admire
The finished cake looks like a little beach island floating above an aquarium.
Your jelly stays bright and wobbly, the fish look like they’re really swimming, and the sandy cake on top is guaranteed to get gasps.
And best of all?
Kids absolutely love it — yours did an incredible job decorating!
