A sensor to measure depth underwater

Does anyone know of sensor which measures depth?

You can do it ultrasonically, like a fish finder does.
You can do it with a pressure sensor and measure the head pressure of the water.
You can do it with a “bubler”. It bubles air through a pipe. The pressure required to make the bubles is proportional to the height of the water.
You can do it with a “displacer” which will change weight according to liquid level.

Jaguarjoe gave a pretty good answer, but to get more & better answers we need some clarification. Do you want to measure how far TO the bottom from your current position? Or… Do you want to determine how deep you are under the surface? What max depth do you need to measure to, and how much resolution do you need?

If you don’t want to cobble together your own (and probably low power=short range) ultrasonic depth finder, you should be able to wire up to a small boat depth / fishfinder transducer. They have a few hundred (or even low-thousands) Watt pulsed output to achieve multi-hundred foot ranges. Pulses are short, total average current draw isn’t too bad.

to clarify, i want to know how deep i am from the surface, although if i had to i could use the depth from the bottom and convert it somehow. as for max depth nothing more than 120’, and as for resolution to the nearest foot would suffice.

If you haven’t already guessed this post goes along with the post for measuring velocity underwater as well, with the goal of having one device measure speed, depth and temperature. The temp part is pretty simply, but i’d also like to add velocity and depth and make it compatible with the arduino.

thanks for any input.