I like what I have pretty well for what I do with them. I think a person needs to know what he expects of them to design them right. For example if you plan on seining them make sure the pond is the correct shape/depth/bottom type.
I think my 1/20th acre pond is as small as I would want to go and try to maintain a fish population. Smaller would be ok for raising seasonal forage or something like that but the smaller the pond the more intense any changes that can happen will happen. For example water exchanges is something to be very mindful of in the design. This 1/20th acre forage pond I lucked out and got about the right amount of runoff and most of it is from my graveled farmstead watershed. The amount of watershed (assuming a watershed pond and not one filled by well or water table) is important because too little and your pond gets low. In a small pond that low level can be even more critical than a larger BOW. Also too little watershed means not very much flow through. This small pond is chocked full of mostly RES and GS. I feed them and that means fertility buildup. With little flow through that fertility builds and builds and becomes a problem. With occasional flow through with adequate watershed runoff this excess nutrients gets flushed out. That is very helpful in maintaining quality water.
Now the other side of the coin. Too much water and flow through. This can be very challenging and stressful on the fish in the pond. This describes my 1/10th acre sediment pond. Being a sediment pond to protect my main pond from sediment runoff, its purpose in life is to take large water flows, slow them down, and give the water a chance to give up anything unwanted from getting into the main pond. So by its nature it can have huge water amounts pass through the pond. This can make the water quality go from anything from perfect to mats of FA because of excess nutrients (in periods of low rainfall and therefore low flow through) to nearly all new, turbid water loaded with sediment. The point is, a pond with huge fluctuations of water flow through can be very challenging for the fish living there. They can go from nice water to abrupt temperature change water to nasty water in a matter of hours or even minutes. This is tough on fish.
My 1/20th acre forage pond and 1/10th acre sediment ponds are only about 50' apart. Yet the nature of the two ponds differences are like night and day. They both raise lots of fish but the sediment pond can have wild swings and even some partial or in one case nearly total fish kill (because of my dumb management mistake of the watershed).
In my three acre pond a big rain event might create a water exchange event on the order of 10 or 20% of the pond water over a day or two. Probably similar for my 1/20th acre forage pond although I have never actually tried to figure either. By contrast my 1/10th acre sediment pond could have several 100% water exchanges in a single 24 hour period in a big rain event. So one very critical aspect of a small pond (in my opinion) is managing the water shed so it is the best size for the pond and the anticipated runoff amounts for your particular area. The smaller the pond, the more critical. I have what I call the Pre-sediment pond just ahead of my sediment pond. I don't really even call it a pond any more as I have connected it to the sediment pond (via a 6" underground pipe) but it used to be completely separate. It is about 20 feet wide and 50 feet long and catches 100% of the water that the sediment pond sees (water from a field terrace flows through it before it goes into the sediment pond). It is a size I can clean the sediment out with my backhoe. I had given up trying to manage a pond this size with the flow through it gets. Parts of the year it will raise tremendous amounts of fingerling fish. But one big rain and the water flow through and number of exchanges and any fish 6" or so in size likely will be laying dead on the bank the next day. Just too much extreme water quality changes too abruptly for the fish to handle.
So if there is one thing I have learned from my small ponds it is that water exchanges and the rapidity of the exchanges can make a world of difference on how the pond performs. If you are making a small pond keep this in mind. If it is going to have valuable fish that you expect to maintain a population you might want to arrange diversion terraces to keep excess water out. If it is just for raising seasonal forage fish, it might not make much difference.
The other thing I would say is if you intend to push the pond by feeding expect it to get to carrying capacity quickly. This means the potential for a fish kill. Aeration becomes even more important in a small pond than big pond if you push the pond to its limits. If you let it progress naturally without extra feed, maybe not as much of a problem. But small ponds things can change rapidly in them. This is both an advantage and a disadvantage. This means that things can go from good to bad quickly. But it also means you can make management changes relatively easy and quickly.
That is probably enough for now. Probably put everyone attempting to read this to sleep.
I see no disadvantage (in my acid soils) to the limestone rock lining. In a small pond it is practical to do it.
