I have the same thing behind my pond, so is it a spring?
Been there since the dam was built 2 1/2 years ago. When its 100 degrees outside and everything dried up, there is always water in it, not running, just standing there. My pond seems to hold water fine. Would be curious to hear what some of the pond builders think also?

"I have not failed, I have only found 10,000 ways that won't work"
Thomas Edison