Betty, the kinds of balloons that these folks provide are not of the helium variety or floating sort. These balloons are the long skinny kind that one can twist, bend and tie into all manner of animals, flowers, or other such sculptural figures. The art is in the twisting.

These balloons will generally not float any farther than a strong breeze might carry it and then only at ground level, where it will encounter far too many obstacles in its path with sharp edges. Those edges will ultimately cause the fragile material that the balloon is made of to burst, long before it would be of concern to marine wildlife.

As Don pointed out the prevailing winds blow eastward from here. I doubt that these balloons could get a block from where life was breathed into them without popping.