Nancy, I keep their compartment doors shut until I see them sitting on top of the house each year. They make it very easy for me because they arrive almost the same day of the month every year. Then I open the doors and they set up housekeeping and I don't think any birds we have will bother them then. They are pretty feisty. But you don't want to let some other bird get into their house and set up houskeeping before they do. Then when they say goodbye and leave I clean out their compartments and shut the doors again until the next year. This year hubby and I left for 2 weeks before they left. The day we returned we were out by the pond and they flew down around us twittering, very obviously saying goodbye. The next day they were gone. It was as though they were waiting for our return to leave. I haven't had any problems so far... We are planning to put up more houses for them next year. Glenda

liz - The pond itself is shaped like a kidney bean and the pond liner is square. So when I laid out the liner I adjusted the extra liner to come out on the corner of the pond where I intended to put the waterfall. The waterfall itself is backed by the extra liner with the end of it tucked into the top of the cement blocks. I was lucky in finding a rock with a lip to cover the ends of the hoses that feed the water fall. It did take me a couple of weeks to adjust the liner to stop leaks but now it is virtually leak free. I am really glad I didn't cement the rocks together because since this post I have had to take it apart 2 times to correct problems. Hopefully, I won't have to a third time! nova

just another note... ... ... use the calculation of 300 GPH for each square inch of water flow. If your spillway is falling on to a smooth surface like flagstone then a water flow of 0.5-0.75 inches will be just fine, which means if your waterfall is 22 inches that comes out to 3,300 GPH, your pump, the best on the market right now, will give you that half inch of water. Now the rougher the creek bed the deeper the flow needs to be, so if you are sticking with this pump you will need to narrow the creek bed to increase the depth of water the larger the river rock the deeper the water. In addition the the greater the lift, the vertical from the pump to the top of the waterfall, will reduce the flow rate so don't make it too high or you will be disappointed in the amount of water flow. By the way this is one of the two best pumps on the market right now. At $0.10 a Kilowatt hour this pump only cost $0.03 and hour to run. The other pump that is great is its sister the AquaSurge Pro 5K-8K.

I was just thinking the same thing as chas045. Last winter was our first with our new pond. We'd just completed it in fall. We didn't know if we should keep the waterfall running over the winter, but before we could make other plans we got lots of snow & sub-freezing weather that didn't stop until there was ice on the sides of the waterfall stream. By then it was too late to drain the filtration system so we just continued to run it all winter, and there was nothing we could do about the ice build-up. Anyway, in spring we noticed the pond losing water much faster than normal. What we discovered was the ice (or combination of ice & dirt settling on the new waterfall structure) had cracked the mortar around the rocks that formed the sides of the waterfall on one side, right at the top, and also right under the waterfall box (see close-up pic). The dirt-covered structure in the upper right is the waterfall spillway. Ice formed mostly on one side, as you can see in the photo, and that's the side that eventually leaked. We are in VA so you could have it even worse in MN, even without your waterfalls running in winter. This allowed water to seep behind the rocks. Once it got behind those rocks, it made it's way down behind all the rocks on that side - between the rocks & the liner. But then near the bottom of the waterfall we had a steeper section & the water made it's way over the top of the liner & out of the pond. Once some of the rocks hiding the liner were removed, we could see where the water was running over the top. We never could tell it was leaking by looking around the landscaping there either, as it never appeared wetter than elsewhere.