Shadows in the Water — Kathryn Lasky

[shared copy] The Starbuck family is anything but ordinary. There are two sets of Starbuck twins: preteens Liberty and July, and their little sisters Charly and Molly. But even more extraordinary is the fact that all four children have the ability to teleflash—they can talk to each other without saying a word! It's a power that comes in handy whenever these adventurous kids are on the trail of a villian. When the Starbuck family moves to a houseboat in the Florida Keys, Liberty and July discover they share a wonderful telepathic link with the dolphins in the area. When they find that someone is poisoning the water with toxic waste, and that the creatures of the Keys are dying, the twins must stop the culprits before it’s too late.