if possible, ship back until you can get hold of the elastic, do this at an angle though or else your top set can get pulled off.
get hold of the elastic and pull for the break. As paul says, make sure you do this underwater, if thats not possible look the other way or you can end up with a pole float bristle in your eye
Good thing about the pole is you can try pulling initialy from every diferent angle, dont forget to try putting an extra section or two on so you can also pull (push) away from you, this often does the trick