Not sure if you're looking for ignoramuses to reply. I assume so, so here I am.

It's probably best to start with posting pictures of the pond. And/or some rough dimensions, plants, waterfalls, number and kind of fish would be helpful. Look around the edge of the pond to see if you can spot anything man made. Skimmer, filter, pipes, covers, etc.

Water flowing would normally be controlled by a pump. The pump can be in the water or someplace outside of the pond. Pumps inside a pond are more common and have a long (15-20') power cord that plugs into a normal outdoor electrical outlet. So you could look around any outdoor outlets to see if there are any plugged in or unplugged power cords laying about.

If plugged in and no water flowing the GFI may have tripped. Pump could be clogged. Possible the previous owners took the pump with them. That's a gray area real estate wise, but pretty uncool in my book.

As far as future maintenance that really depends on what you want. Just a simple feature? You like gardening and want to get into water plants? You like fish and want to get into that hobby? If you ask 100 people you will get 100 different answers because almost everyone is going to tell you how they keep their pond. So it can be super confusing until you realize they're all talking about different kinds of ponds. Here's are some questions I ask people new to ponds.

I think the worst thing people can do is go to the local pond store and ask a clerk. They will load you up with as much junk as they think you'll swallow. Dumping that junk into your pond can give you actual problems. Truth is most ponds require very little care and almost no products.

The pond may have an auto fill in which case you don't have to worry about adding water. Otherwise in the short term the only thing you made have to do is add water. Assuming city water you have to be a little careful about chlorine. Putting a hose in the pond and turning on the water full is dangerous to fish. And the chance you'll remember to turn it off is almost nil so hours later you'll have a flooded yard and dead fish. A better option is to turn the hose on just for a very slow drip. You'll probably still forget it but much less risk to fish, less flooding, less wasted water.

Hello, waterbug_guy,

Thank you so much for taking the time to reply so promptly! I actually saw your post as soon as you posted it, even as the movers were carrying furniture into the house. One of them found a cord that plugs into an outlet sticking out of the ground and voila! water ran down the stream thing into the pond.

Hours later, though, we discovered that the pond was being drained completely! I suspect there is a leak somewhere--either in the hose that sucks the water out of the pond or the creek thingie where it is made to flow back in. I know it is probably bad for the fish (and later we found, a frog!) but we had no choice but to refill it with tap water using the garden hose.

My first reaction to the pond is to turn it into a literal rock garden where I can grow granite, basalt or anything I won't ever have to think about. But even that will have to wait until other things are taken care of. The frog also kind of made the case stronger in favor of repairing the pond and keeping it instead.

I apologize for taking this long to reply, things have been busy as you can imagine. I attached a snapshot of the pond for you. Thanks from me, as well as from the 7 orange fish-dudes and one frog whose lives you saved.

Pagan

You just need to purchase a bottle of water conditioner for ponds at a pet store as soon as possible. You will at the very least need that on hand as you learn about your pond. Then, when the water gets low you can safely add water. When you are dealing with water loss, either from leaks or splashing or whatever, don't play with it unless you are going to be around home for the day so you can check the water level occasionally and shut it off and refill it as necessary before it gets too low. Two of the fastest killers of fish are a pond with no water, followed by refilling a large amount of the water with chlorinated tap water that is poisonous to them. You can probably take your time learning about your pond and finding the leak as long as you do that.

Sue,

thank you for that information. I have no time to go to a physical store and was planning to get water conditioner from Amazon. Is there a specific kind or brand you can recommend?
A quick search and cursory reading led me to something called API Pondcare Chlorine and Heavy Metal Neutralizer. Will this do? Stop-gap measures are really the only things I have time for at the moment. I am also somewhat worried about winter preparations. I am still adjusting to the concept of winter myself and have no clue if these fish dudes are supposed to be plucked out and put in a jar or something.

Thank you for all your help

The API sounds fine. Whatever brand you can get there the fastest, so you have it on hand for whatever happens. You can even find it at Walmart if there is one near you.

Thing is, adding chlorine a day later will not do anything. First of all, if there was a significant amount of chlorine in the tap water the fish would be dead or seriously sick already. Second thing is, it doesn't take long for the chlorine to dissipate out of the water, especially if the stream or waterfall is running, so there would be no point to add dechlorinator a day later.
If the pond started losing water when you turned the stream of, It's likely the leak is in around the actual stream itself, as this is a common place for leaks to develop. It will probably require you to take the stream apart rock by rock to locate the leak. This will have to be done with the water running so you can see where it is leaking. Generally it gets diverted to the side somehow and into the ground. Find the wet spot on the ground.

No, my recommendation was not meant to mean to add it a day later, but rather to have it on hand the next time in case he has to add a large amt of chlorinated water, if it happens again. Maybe I wasn't clear enough. :)