Most of these ideas require little more than skills with the scissors, and they are something you can make while sitting in front of the TV.
Bubble streamers: find craft paper in various shades of blue, green and purple. If you can buy a few sheets of shiny or glittery paper then it will add an extra layer of glamour. Cut as many circles as you can tolerate in two or three different sizes (such as 3cm, 5cm and 7cm). Remember they do not have to be exact and the chains look better when things are a bit random.
All you need is paper, scissors, ribbon and some stickytape
Find some craft ribbon, curling ribbon or wool and begin taping the circles randomly on the ribbon in long chains. I used between 15 and 20 circles per chain and made about 30 chains. It looks better when you grab the circles randomly so you get a mix of colour and size.
Hang the bubble streamers across doors, windows or individually from the ceiling to create an underwater feel.
Use individual bubbles (preferably from shiny or glittery paper) to add highlight to walls and windows.
By sticking seaweed, bubbles, fish and starfish in the window, it made the room feel like an aquarium
For the seaweed I used stiffened felt from Spotlight but you could just use coloured paper or card. Use a couple of different shades of green and make two different sizes. Blu-tack to walls or windows.
The star fish were gold stars I found in the party section at Spotlight, but you could easily make your own.
I also cut fish out from a piece of $1 wrapping paper and found a fish piņata on sale.
To finish I blew up 40 balloons in shades of green and blue and literally dumped them on the floor.
I also really like this idea for goldfish lanterns if you can find some cheap paper lanterns.
Kids were served fish and chips in disposable noodle boxes while adults were given a platter of sushi.