Looking for some fun Under the Sea birthday party ideas? Well, you can never go wrong with a magical mermaid shell-ebration or a sea creature soirée! The “Under the Sea” party theme is one of our favorites for kids’ birthday parties because there are oceans of possibilities. You can explore all kinds of fun and unique decorations, activities, and party treats.

We’re sharing our best under the sea party ideas and supplies for your next mermaid party or ocean-themed bash. So without further ado, let’s dive in! 

Under-The-Sea & Mermaid Decorations 

Mermaid birthday party decoration ideas.

Photo by Tanja Kopper Photography, Event Planning and Design: His & Her Events

Under-the-sea birthday party balloon installation.

Photo by Tanja Kopper Photography, Event Planning and Design: His & Her Events

Creating an ocean-like atmosphere is crucial for any under-the-sea theme party. The best way to do this is by bathing your backyard or party room in balloons. We love all of the dreamy balloon installations at this mermaid theme birthday bash by His & Her Events

Crafty Hands by Chaviz created an array of bubbly balloon garlands in shades of mint, purple, and peach. (À la Disney’s The Little Mermaid). They also layered translucent balloons, long tentacle-esque balloons, and sea-themed garlands together over the party area. This is an excellent way to make your party guests feel like they’re celebrating underwater! 

Shark-themed birthday party decoration ideas.

Event Planning and Design: But First, Party.

Shimmery tinsel garlands and party curtains are another dazzling under-the-sea decoration idea. A sea of blue, green, and silver tinsel garlands made a fin-tastic addition to our shark party seen above. To get the look, layer the garlands in a wave formation along a backdrop, or drape them above your party table. Play it up by adding a few tropical fish balloons or shark balloons and voilà: c’est la sea!

Mermaid birthday party table decorations.

Photo by Tanja Kopper Photography, Event Planning and Design: His & Her Events

Be sure to extend your mermaid party decor to the table. You can decorate with colorful netting, sea shells, and holographic confetti (a must-have mermaid birthday decoration!) We also suggest lining the tablescape with seashells and an ocean-infused floral arrangement like this one from Angels Petals.

Mermaid birthday party tablescape ideas with iridescent party plates.

Event Planning and Design: The Shift Creative.

For tableware, we recommend these magical watercolor clam shell plates and matching napkins. Or, you can experiment with iridescents and layer this shimmery shell plate with a scalloped blue or pink plate. Either way, don’t forget to complete each place setting with an iridescent party cup and a shiny set of cutlery!

Shark theme party table.

Event Planning and Design: But First, Party.

If your under-the-sea bash is for a boy’s birthday, we suggest dipping into the blue hues. These solid blue plates under small chromatic foil plates are a tide and true pair for any underwater party theme. Just add a few shark-themed party accents and you’ll have yourself a jaw-dropping tablescape!

Under the sea theme party plates.

Under the sea party decorations.

Octopus, lobster, and sea turtle party supplies also make quite a splash! We love the idea of centering an under-the-sea party around these adorable sea animals. Simply add an under-the-sea garland to complete the look. This gender-neutral array is sure to leave any little minnow bubbling with excitement! 

You can also incorporate these party supplies into any mermaid birthday theme by mixing and matching them with your shell plates and napkins. After all, the more party animals, the better!

Under-The-Sea & Mermaid Party Food

Mermaid party food ideas.

Event Planning and Design: The Shift Creative. 

Having the right under-the-sea theme party menu is another great way to set an aquatic ambiance. You can serve simple snacks and appetizers like goldfish crackers and popcorn shrimp. Or, you can go “gourmet” and serve fish sticks and peanut butter and jelly(fish) sandwiches. Either way, we suggest getting creative with your presentation and adding a “seaweed” garnish, like parsley, to each dish.

Shark party birthday cake.

Event Planning and Design: But First, Party.

For dessert, an oceanic birthday cake is a must-have for any sea-themed soirée. You can take a modern approach and serve a blue cake with wavy gold frosting embellishments.

Mermaid birthday cake ideas.

Event Planning and Design: The Shift Creative.

And if you’re making a mermaid birthday cake, we recommend decorating it with mermaid cake toppers and mermaid tail lollipops.

Under-The-Sea & Mermaid Party Activities

Mermaid birthday party activity ideas.

Photo by Tanja Kopper Photography, Event Planning and Design: His & Her Events

One of the best things about this theme is that it’s full of fun party activities to explore. Water games or pin the tail on the mermaid are classics and work well for a variety of age groups. For fêtes with slightly older fishies, we suggest including a craft like painting mini jewelry boxes. 

Not only is this a wonderful mermaid birthday idea, but these little trinket boxes make the perfect party favors. You can even elevate the excitement by filling each box with mermaid hair clips or temporary tattoos!

Mermaid birthday party ideas and mermaid birthday party decoration ideas.

Photo by Tanja Kopper Photography. Event Planning and Design: His & Her Events. Balloons and Ceiling Installation: Crafty Hands By Chavis. Kids Event Rentals: Bay Area Kid Rentals. Florals: Angels Petals. Under The Sea Backdrop and Swing: Petite Events Co. Professional Disney Character: Smile And A Song Princess Parties. Face Painting: Catalyst Arts. Linens: Pleasanton Rentals. DJ, Lighting, Bubble and Fog Machine: Entourage Events SF. Clear Tent: Unica Party Rentals. Crepe Cart: Eats A Crepe. Cocktails: Manhattan Zodiac. Birthday Cake: Doodle Cakes Bakery.

Mermaid birthday party table with mermaid decorations.

Event Planning and Design: The Shift Creative.

We hope these ideas have inspired you to take your party under the sea. For even more inspiration, take a deep dive into the rest of our mermaid party and under-the-sea party collections. From our fête to yours, bonne chance!  

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