Very impressive setup you have there. I would call that a stream/pond. Or how about a RIVER and pond. I doubt that splash could cause your loss, but that is one huge flow. I would suspect an underground loose or cracked fitting which will probably be very hard to find. I would wait until things dry out (assuming you get less summer rain), hoping to find the muddy spot that you may easily have overlooked.

I have 25' stream and am always finding slow overflows as ground settles or the dog, or me, stands on the edge. It is much easier to find when the ground is already dry. I doubt that your installers would have risked leaving edges as low as mine, but setting all those heavy rocks could have ripped the liner.

Thank you, I have a feeling that the heavy rocks could of did it. My father informed methey added a coupling extension to my main line last time they were here. I fear that in the cold weather it didnt seal properly. I will have to check the sides for any ground settling. Thank ou for the reply.

When you're checking for leaks, when do you do it? I've got a smaller-than-that pond, but a very long stream & like chas045, what I've found is I lose water via slow overflows on the edge. But, for my stream, by the time I notice the water loss, there's not much wet earth to show for it--I think what's going on is as the water in the pond drops, the pump is pumping slightly less so it doesn't overflow the banks, so they dry up. I've found I need to check about 2-4 hours after refilling the pond.

Do you have any control over the water going up? Can you divert it & run, say, half the stream--or 2 of the 3 waterfalls--just to try to see if you can get some idea where the leak is? Figuring that if adding a section to the non-leaking pond doesn't cause water loss, it doesn't have your leak in it.

Good luck, your description sounds wonderful!

I want to second meganmca about diverting part of the stream so that the leak/overflow area can be isolated. I'm not sure why I forgot to mention it before. Since you may have to get down to your piping anyway, you could attach a new section of pipe as close to the waterfall as possible and return it to the pond directly by resting the pipe on top of the strream. Then if no leak continues, remove sections of pipe one by one until the spill section is found. Of course, if the direct return shows a leak, then the leak is in the underground piping. In your case, that is some hefty pipe and won't be as trivial as my case using 2" pipe for 25 feet, pipe I already had on hand. Perhaps you have some old gutter material that could be used as a diversion return?