A baby shower theme should be easy to shop for and easy to picture the second someone hears it. Under the sea checks both boxes. It works for a boy, a girl, or a shower where nobody knows yet, and you can build the whole thing around whatever’s already sitting in your linen closet in blue.
Below are 21 ideas covering decorations, food, drinks, games, favors, and a few small touches that pull the whole party together. Pick and choose based on your budget and how much time you actually want to spend gluing things.
Decorations That Set the Underwater Scene
These are the pieces that do the heavy lifting the moment guests walk in. You don’t need all four, but even two of them will make the room feel like a theme instead of a few scattered balloons.
1. Clear Bubble Balloon Garland
Fill clear balloons with a few sprinkles of light and dark blue confetti so they look like water and rising bubbles instead of plain party balloons. Twist them into a garland along a wall or drape it over the food table for an instant “we’re underwater” backdrop.
The clear balloons do more work than solid-color ones because they actually read as bubbles from across the room, not just as balloons in a color scheme. Mix in a few white and silver ones for shimmer.
A DIY kit with balloons, tape strip, and glue dots runs about $15–$25 depending on garland length, and one person can put it together in under an hour.
2. Fishnet Table Runner with Starfish
Lay a real or craft-store fishnet down the center of your food or gift table, then tuck starfish, small shells, and a scatter of sea glass into the netting. It’s one of the cheapest ways to make a table look intentional instead of thrown together.
Because the net has texture and depth, it photographs better than a flat runner, and it hides table seams or a slightly mismatched cloth underneath.
Craft store fishnets cost around $6–$10, and a bag of mixed starfish and shells adds another $10.
3. Paper Jellyfish Lanterns
Paper lanterns with crepe paper streamers hanging underneath make surprisingly convincing jellyfish, especially in a mix of white, lavender, and pale blue. Hang a cluster at different heights over the dessert table or entryway.
They add height and movement to a room without taking up any table space, which matters if you’re already tight on surface area for food and gifts.
A set of five to seven lanterns with streamer material costs roughly $20–$30 and can be assembled the night before.
4. Mermaid Tail Welcome Sign
A large printed or painted sign shaped like or featuring a mermaid tail at the entrance tells guests exactly what party they walked into. Something like “Welcome Aboard, We’re Having a Whale of a Time” gives it personality without being overdone.
Mount it on foam board so it stands on its own near the door or gift table, and it works as a photo backdrop prop afterward too.
Printable versions from Etsy run $8–$15 for a file you print yourself at a local copy shop.
A Cake and Sweets Table Worth Diving Into
The dessert table is usually the most photographed spot at the party, so it’s worth putting a little extra thought here even on a tight budget.
5. Ombre Wave Cake
A two or three tier cake frosted in graduating shades of blue, from deep navy at the base to pale aquamarine at the top, mimics ocean depth without needing any fondant sea creatures at all. Add a few edible pearls or a single fondant starfish for the finishing touch.
This works well if you’re ordering from a local bakery rather than a specialty cake artist, since ombre buttercream is a common skill and doesn’t require custom sculpting.
Expect to pay $50–$90 for a two-tier cake depending on your area and serving size.
6. Fishbowl Cupcakes
Top blue-frosted cupcakes with a gummy fish and a few crushed graham cracker “sand” crumbs pressed around the base. They’re simple enough to make at home the night before and don’t require any special decorating skill.
Guests can grab one without needing a plate or fork, which keeps the dessert table moving during a party where most people are standing and mingling.
A batch of two dozen costs under $20 in ingredients if you’re starting from a box mix and store-bought gummy fish.
7. Seashell Macarons
Pastel macarons piped or pressed into a shell shape, with a small edible pearl tucked in the center, look far more elaborate than they are to make. Bakeries also sell these ready-made if baking macarons isn’t something you want to attempt before a party.
They hold up well at room temperature for a few hours, which matters for a shower that might run two to three hours without refrigeration nearby.
Pre-made sets of a dozen typically run $18–$30 from a local bakery or Etsy seller.
Savory Bites With Ocean Flair
Finger food that people can eat one-handed while holding a drink and chatting works best for a shower crowd. These lean into the theme without requiring a full seafood spread.
8. Crab Salad Croissant Boats
Fill mini croissants with a chicken or crab salad and add two small candy eyes on top with a toothpick to turn each one into a tiny crab. It’s a small detail, but it’s the kind of thing guests remember and photograph.
Because they’re bite-sized, they work well on a passed tray or laid out on a platter without needing individual plates.
A batch of 24 mini croissant crabs costs around $15–$20 in ingredients, most of which is the croissants themselves.
9. Pufferfish Fruit Platter
Start with a whole cantaloupe or honeydew, add grape or blueberry eyes, and stick toothpicks with grapes and pineapple chunks all around it like spikes. It looks far more impressive than the ten minutes it actually takes to assemble.
It also doubles as a centerpiece, so it earns its spot on the table twice — once as decor, once as food.
One melon and a bag of grapes runs about $8–$12 total, making it one of the cheapest showpieces on this list.
10. Shrimp Cocktail Sailboats
Skewer a grilled or chilled shrimp with a small triangle of white cardstock threaded on as a “sail,” then stand it up in a shot glass or small cup of cocktail sauce. Line up a dozen on a platter for an easy, elegant appetizer.
This one leans more upscale than the others, so it’s a good pick if your shower guest list includes people you want to impress a little, like in-laws meeting the theme for the first time.
Jumbo shrimp run $12–$18 per pound depending on your area, and a dozen shrimp is usually plenty for a shower-sized crowd alongside other food.
Drinks That Feel Like the Sea
Two drink options is usually enough for a shower — one for people who want something sweet, one lighter option for anyone avoiding extra sugar.
11. Blue Lagoon Mocktail
Mix lemon-lime soda with a splash of blue raspberry syrup and a squeeze of lime for a bright, ocean-blue drink that photographs beautifully in a clear glass. Add a gummy fish or a paper umbrella for the finishing touch.
Because it’s non-alcoholic, it works for the whole guest list including the mom-to-be, which is really the whole point of a shower drink.
A 2-liter bottle of soda and a bottle of blue syrup runs about $10 and easily serves 20–25 guests.
12. Coconut Pineapple Wave Punch
Blend coconut water, pineapple juice, and a little sparkling water for a lighter, less sugary option than the blue lagoon drink. Garnish with a pineapple wedge or a small paper sail for a nod to the theme.
This one tends to disappear fast at daytime showers, since it reads more like a refreshing drink than a dessert-adjacent one.
A batch large enough for a punch bowl costs roughly $15–$20 in juice and coconut water.
Games and Activities Guests Actually Enjoy
Skip anything that puts one person on the spot for too long. The best shower games move fast and give everyone something to do at the same time.
13. Guess How Many Fish in the Jar
Fill a clear jar with fish-shaped crackers or small toy fish and have guests write down their guess as they arrive. Whoever gets closest wins a small prize, and it’s a natural icebreaker for the first twenty minutes before everyone’s settled in.
Because guests fill in their guess on the way in rather than during a structured game segment, it doesn’t eat into your schedule at all.
A large jar and a bag of fish crackers costs under $10 total.
14. DIY Onesie Decorating Station
Set out plain white onesies, fabric markers, and a bin of ocean-themed patches or iron-on stickers, and let guests decorate one each for the baby’s wardrobe. It gives people something to do with their hands while they chat, which works especially well for shyer guests.
The mom-to-be gets to take home a stack of one-of-a-kind onesies at the end, which tends to mean more than a store-bought outfit.
Plan on $4–$6 per plain onesie plus $15–$20 for a shared bin of markers and patches for the whole group.
15. Under the Sea Bingo
Printable bingo cards featuring baby items — pacifiers, bottles, tiny socks — dressed up with an ocean border keep everyone playing through the gift-opening portion of the shower instead of scrolling their phones. Mark a square each time a matching gift gets opened.
It’s a low-effort way to keep the whole room engaged during the part of a shower that can otherwise drag for guests who aren’t close friends of the mom-to-be.
Printable card sets typically cost $6–$10 for enough copies for a full guest list.
Favors Guests Will Actually Keep
The best shower favors are small, useful, or at least pretty enough to sit on a shelf instead of getting tossed in a junk drawer.
16. Starfish Soap Favors
Mini handmade soaps shaped like starfish, tied with a simple ribbon and a thank-you tag, are practical enough that guests actually use them instead of letting them collect dust. Scented with something ocean-adjacent like sea salt or coconut ties it back to the theme.
Because they’re small and lightweight, they’re also easy to set out as a tablescape element before guests take them home.
Bulk orders of 25 starfish soaps run around $25–$35, which comes out to roughly a dollar per guest.
17. Message in a Bottle Thank-You Notes
Small glass bottles with a rolled-up thank-you note tucked inside make a favor that doubles as a keepsake. Guests can display them on a shelf long after the shower is over.
They also work well lined up along the gift or dessert table before the party ends, so they’re doing double duty as decor and favor at once.
Small glass bottles cost about $1–$2 each in bulk, so a set of 20 runs $20–$40.
18. Mini Sand and Shell Jars
Layer sand and tiny shells in a small mason jar for a favor that takes five minutes to assemble but looks like it took much longer. Add a twine bow and a small tag for a finished look.
These are one of the cheapest favors on this list because the core materials — sand and shells — are often already sold together in craft store party sections.
A bag of craft sand and mixed shells covers about 20 jars for roughly $15 total.
Personal Touches That Tie It All Together
These aren’t decorations exactly — they’re the small choices that make the shower feel planned around this specific mom-to-be instead of a generic theme kit.
19. Wave-Shaped Invitations
Invitations cut or printed with a wavy bottom edge, featuring a sea turtle, octopus, or seahorse illustration, set the tone before guests even arrive. A line like “Join us in making a splash” on the front gets guests excited before they RSVP.
Digital versions let you send them instantly and skip printing costs entirely if your guest list is mostly reachable by text or email.
Editable templates from Etsy typically cost $6–$12 for unlimited prints or digital sends.
20. Baby Book Guest Book
Instead of a traditional card, ask guests to bring a children’s book with a note written inside the front cover. It builds the baby’s first library and gives the parents something to actually read together once the shower is over, unlike a stack of cards that usually gets tucked in a drawer.
It also solves the awkward “what do I write” problem, since most guests find it easier to write a note in a book than sign a generic card.
There’s no added cost to the host — guests typically spend $5–$15 on a book they were already planning to buy anyway.
21. Mermaid Sash for Mom-to-Be
A simple sash reading “Mom to Bee” or “Under the Sea and Ready to Be a Mommy” gives the guest of honor something that sets her apart in every photo without requiring a full costume. Pair it with a small shell or starfish crown for photos during gift opening.
It’s an easy way to make sure she’s instantly identifiable in group shots, especially useful if the shower is large enough that not every guest knows her by sight.
Sashes typically run $10–$18 on Etsy and can be personalized with a name for a few dollars more.
Twenty-one ideas is more than enough to build a full party around — most hosts land on six to ten of these total once decorations, food, one or two games, and favors are covered. Start with whichever ones fit your budget and your guest list size, and build out from there.