When he determined that Eliza had heard him, Phineas gulped one more breath of air and submerged his head in the water, opening his eyes to reacquaint himself with his surroundings. He spotted the craft two dozen feet below him. He kicked down as he began his descent, stopping every several seconds to allow his body to readjust to the pressure. The oil stream twirling past him, he finally reached the hovercraft, buried half in tidal sands. The back door was exposed, but as he pulled on it it refused to budge until he braced both of his feet on either side and forced it open. A storm of bubbles cascaded past him, but the interior was dark. Increasingly low on air, Phineas kicked upwards to the surface and burst out, gasping air until he could dive down again. A small stream of bubbles began to flow out of the tube in his hand, which meant that Eliza had already started blowing.
[i]Better early than late...[/i] Phineas thought, and reached the door to the craft again. He managed to push aside the debris blocking the interior and swam inside. The oil tank was easy to find due to the stream of leakage, and Phineas jammed the end of the tube into it. To his surprise, it was a perfect fit. He turned to leave, but a shape illuminated by the rays of sun outside stopped him short. 
An electric eel hovered patiently outside the hovercraft door.