Someone's been partying out at sea... I recently walked along the beach at Covehythe and found 72 balloons washed up on the shoreline. Balloons released in the south-east nearly always end up out at sea because of the prevailing southwesterlies. Wherever they land they cause a major hazard to wildlife, but particularly at sea where they can either entangle sea creatures or can be swallowed having been mistaken for jellyfish (turtles' main food source).
Here's what I found:
Balloons don't just injure wildlife out at sea - a swift fell from the sky into my garden last summer, having flown into a latex balloon from a charity balloon release, which burst around its neck and wings... (this bird was lucky - we were on hand and able to release it...)
For more information see the Marine Conservation Society's Don't let go campaign.