Just as the lower gate was being swung open to admit them to the lock, there was a cry of warning from above.
"What's that?" cried Joe.
"I don't know," Blake answered, "but it sounds as though something were going to happen. I didn't have all those feelings for nothing!"
Then came a cry:
"The upper gate! The upper gate is open! The water is coming down! Put the emergency dam in place! Quick!"
Joe and Blake looked ahead to see the upper gates, which were supposed to remain closed until the boat had risen to the upper level, swing open, and an immense quantity of foamy water rush out. It seemed about to overwhelm them.
CHAPTER XVIII
THE BIG SLIDE
For a short space there was a calm that seemed more thrilling than the wildest confusion. It took a few seconds for the rush of water to reach the Bohio, and when it did the tug began to sway and tug at the mooring cables, for they had not yet been cast off to enable it to be towed.