“There goes the emergency dam!” suddenly cried Blake.

“Gone out, you mean?” yelled Joe above the roar of waters.

“No, it’s being swung into place.  It’ll be all over in a few minutes.  Good thing we got the pictures when we did.”

Across the lock, about two hundred feet above the upper gate, was being swung into place the steel emergency dam, designed to meet and overcome just such an accident as had occurred.

These dams were worked by electricity, and could be put in place in two minutes; or, if the machinery failed, they could be worked by hand, though taking nearly half an hour, during which time much damage might be done.  But in this case the electrical machinery worked perfectly, and the dam, which when not in use rested against the side of the lock wall, and parallel with it, was swung across.

Almost at once the rush of water stopped, gradually subsiding until the tug swung easily at her mooring cables.

“Whew!” whistled Blake in relief, as he ceased grinding at the crank of his moving picture camera.  “That was going some!”

“That’s what!” agreed Joe.  “But I guess we got some good films.”

“You certainly deserved to!” exclaimed Mr. Alcando, with shining eyes.  “You are very brave!”

“Oh, it’s all in the day’s work,” spoke Blake.  “Now I wonder how that happened?”

“That’s what I’d like to know,” said Captain Wiltsey.  “I must look into this.”

An inquiry developed the fact that a misplaced switch in some newly installed electrical machinery that controlled the upper lock gate was to blame.  The lock machinery was designed to be automatic, and as nearly “error proof” as anything controlled by human beings can be.  That is to say it was planned that no vessel could proceed into a lock until the fender chain was lowered, and that an upper gate could not be opened until a lower one was closed.  But in this case something went wrong, and the two gates were opened at once, letting out the flood.

This, however, had been foreseen, and the emergency dam provided, and it was this solid steel wall that had saved the lock from serious damage, and the Bohio from being overwhelmed.

As it was no harm had been done and, when the excitement had calmed down, and an inspection made to ascertain that the gates would now work perfectly, the tug was allowed to proceed.

“Well, what are your plans now, boys?” asked Mr. Alcando on the day after the lock accident.

“Back to Culebra Cut,” answered Blake.  “We have orders to get a picture of a big slide there, and we’re going to do it.”

“Even if you have to make the slide yourself?” asked the Spaniard with a short laugh.

“Not much!” exclaimed Blake.  “I’d do a good deal to get the kind of moving pictures they want, but nothing like that.  There have been some rains of late, however, and if things happen as they often have before in the Cut there may be a slide.”