Imagine a school of fish weaving through a network of pipelines at the bottom of a bay. Only instead of live fish foraging for food, these are robots patrolling for damage and pollutant leaks. Robo-fish can fit in places divers and submarines can’t.

The first robotic fish, built in the 1990s, were around 4 feet long, had thousands of parts, and cost thousands of dollars. The newest, designed by MIT researchers Kamal Youcef-Toumi and Pablo Valdivia y Alvarado, are 5 to 18 inches long, have about 10 parts, and cost just hundreds of dollars.

These sleek robots are made of a seamless, synthetic compound engineered to be flexible in places where fish bend a lot – the tail _and rigid where they don’t – the midsection. A single motor sends a wave down the interior, and the motion of the material mimics the swimming motion of a real fish.

Although the latest robotic fish are pretty close to making a splash, they are not yet swimming in lakes and oceans. It’ll be a few more years before you can tell the story about the robo-fish that got away.