Animating the water would probably be the hardest part... I guess it would depend on how good you want it to look.
If you wanted to do it yourself, you could make it look fairly good with just Photoshop and Wondertouch ParticleIllusion (using their free trial) You could start by cutting out the part of the bridge you want to fall in the water, making it a separate image. Use clone brush to fill in the missing piece behind where the bridge way.
Rotoscope the separate image in your editing software so it falls the way you want it to. Export the file (unfortunately PI does integrate with other software)
Animate the explosion, smoke and water in ParticleIllusion. The website has tons of emitter files for you to experiment with and find the right fit for your scene. Export that...
Then back in your editing software, you can add camera shake, color correction, anything else to make it look more realistic.
With some creative editing, you'll be able to sell the illusion pretty well. This isn't the only way to do it, but it's probably one of the cheaper routes. Good luck =)
Just do it practical bro