ultrasonic sensor

Hi,
I am a newbies, this is my first project with micro controller. I did search this forum to find the solution to my problem but couldn't find it.

I have an ultrasonic sensor, that I intended to use it in measuring the water level of a river. The sensor give an analog output 4~20mA. What I understand from example, Arduino board read Voltage not Ampere. So could anyone help me, Thanks

Put in a load resistor,and measure the voltage across it.