The garden pond is overflowing into the unknown. How do I find out where it goes?

For a few years now, we have had a house on a hillside and feel comfortable in it. On the east side, a small pool is attached, in which goldfish live. When it rains, water runs into it, but it never gets fuller than it is - that means somewhere there is an overflow or a leak. I wonder that it is even so tight (the way it looks), but it is. :cool: The wastewater does NOT go into the public sewage system, but seeps away ... I have no idea where that could be ... and unfortunately no idea how to find out. When it rains and the water (presumably) runs somewhere into the garden, it is of course always everywhere wet and I cannot tell if the dampness might be coming from the pool or from the sky. The garden is about 600 sqm (visible from above in one of the pictures) I once drained the pool far down (the fish and newts were housed with the neighbor in the meantime), but at the bottom, it is quite muddy (with lotus plants blooming again and again) and I have not found any outlet (it should actually be at the level of the water surface). As long as it goes like this, it's okay, but I would really like to know where the excess water goes. I assume there is no trick (like with a bicycle tube, "dipping it in water" to find the leak), but I still want to try: Does anyone have an idea how I could solve this mystery?

When it rains and the water (presumably) runs somewhere in the garden, it is of course always wet everywhere and I cannot tell if the moisture might be coming from the pool or from the sky.

In bright sunshine:
1. Hang in the hose and turn it on
2. Open a beer and sit next to it
3. Observe

Even if you don’t find anything out, you tried :cool:

Good idea. I haven't thought of that before because water here (North Hesse) is quite expensive (which is why we operate the rainwater system). But for this purpose, I will think about it again :cool: Thanks

If you scoop out 5 jugs/buckets when it’s raining and use them when it’s sunny,
it costs nothing

There is so-called leak detection dye, which is a water-soluble powder that colors your water, e.g., neon pink. It is actually intended for problems in the house. However, it should also be easily visible in the garden to see where the water from the pond ends up. It also exists in versions that can only be seen with a UV lamp, so not everything stays colorful forever.

Since it is also meant for roofs and terraces, it should actually be environmentally friendly. However, if you are talking about fish - they would certainly have to be caught briefly and then the water would have to be changed again.

5 buckets will hardly be enough. Because I "normally" don't know any "source" in the garden (meaning no place where it bubbles out), I assume it would need far more inflow. ... but the idea "in sunshine" is probably the right one.