A pond used for swimming will be all the better for having a sandy beach. Kids especially appreciate a waterside"sandbox" and they'll be more likely to spend time in and near the water if they're not ouching on sharp stones when they step on shore and in the water. Beaches can be built at the same time the pond is constructed, or added afterwards, quick-style with a truckload of sand, or longer lasting with some digging and foundation fabric. Add a picnic table, beach chairs, an umbrella, a barbeque, maybe a water slide, and you can vacation at home -- everyday!
Beach sites are usually relatively flat shore areas, so the sand on shore and in the water creates a platform for easy walking into the water; and inhibits the tendency of sand to slide off the land and into the water and further into the pond, creating a need for more sand. Flat or gradual sloping areas also make for pleasant areas for sunbathing, kids' play, etc. Some pond owners float a string of buoys on the water to demark the safe swimming depth, for kids.
Beach location also involves orientation. I find that beaches often have several things in common. On the path from house to pond, they are often at one of the first pond areas you reach. They tend to be oriented toward the sun, that is, to the south. They are likely to be in the open, rather than under tree branches. In addition to good light exposure, this avoids a lot of leaf drop on the sand. Beaches should not be sited where they will receive much watershed runoff, or be at the receiving end of a drainage ditch, stream, etc. This avoids problems of sediment runoff, erosion, washing away sand, etc. It's not a good idea to locate a beach near the pond overflow spillway, whether it's a pipe or natural earthen channel. These areas can pull in debris/leaves via the outflow current. Beach builders also try to avoid prevailing downwind locations, to avoid washed up debris. There is usually access for deliveries of sand for initial beach creation, and periodic sand replenishment.
There are lots of ways to build a beach, from simple to elaborate. Simple is to just dump a load of sand on the shore (by pickup or tractor bucket, etc.) and spread around. Sand should be sufficient to cover the planned shore area plus enough to push (shovel, rake, tractor, etc) into the water to create a sandy underwater area. I find that when you step into the water you will appreciate soft sand underfoot rather than sharp stones and/or mucky mud. How wide you make the beach is your choice, but about 10-20 ft wide usually does the trick, or more as you wish. And how much underwater area you want to cover is also optional, but it's nice to be able to walk in on sand in water up to your waist or deeper, before you dive in. The underwater area will also depend on slope. The steeper the slope the less likely you will extend sand far into the pond, especially since steep drop offs tend to allow the sand to slide away into the pond, needing frequent resupply. Kids like sand on shore and in the water. A nice sandy beach will go along way to making a pond a favorite place for kids.
Types of Sand
If you've been to a few natural beaches you'll note that sand texture varies from powdered-sugar fine white to grainy pebbly sorts, even black sand. But for beach builders you'll probably be buying sand from a construction supplier, and manufactured fine grain washed sand is a good choice. It's often called masonary sand, and it should be washed as opposed to bank run sand from a river bed. Why? River bank sand is cheaper, but it probably contains silt and other organic matter that will cloud your pond water and take some time to dissipate. You'll be reminded every time you step in the sand and see silt cloud the water. Pea stone and granite/stone dust is sometimes used.
If you want a longer lasting beach than simply a layer of sand dumped on the shore, consider digging out the area and laying down a foundation fabric of porous geo- textile. This is usually a one foot deep bench the size of the desired beach, both on shore and in the water. Of course this is best done with the water drawn down to expose the work area. The fabric will prevent dirt from mixing with the sand, so the sand will last longer, and the fabric will resist weed growth. Weeds will probably arrive sooner or later, but they should be easy to control with some weeding and raking. Some people use plastic sheeting for a base, thinking it will better prevent weed growth. True enough, for a while. But eventually, whether you use porous fabric or plastic, weeds can grow in the sand or through the fabric. Besides, plastic sheeting is apt to allow rain water to puddle up on the beach.
Some beach builders recommend using enough sand so it sits higher than the flanking grassy shore. Especially on the upslope side this acts as a berm to deflect runoff from washing into the beach. To make a really effective berm against damaging runoff, install either wood beams or stone to frame the beach, especially on the upslope side.
Also often recommended is to create a berm at the bottom of the beach, underwater, to hold the sand in place. This is sometimes done with the soil dug out of the bench, or wooden beams, etc. The idea is to create a speed bump at the bottom of the beach to hold the sand in place.
Topics vary from month to month and provide great information when researching where you want to build a pond, or how to keep it clean. Other areas of interest are pond use for more than swimming, and how to keep fish happy in your pond.