This will be an interesting and maybe frustrating project for a first time pond owner. The link above (and following) makes it all sound pretty easy.
http://www.grit.com/Tools/Build-Your-Own-Natural-Swimming-Hole.aspxNot really so. To make the pond a clean swimming pond it takes a lot of work to keep it clean and to not resort to turning it into a chemical dump keeping it "clean". I have quite a bit of experience with numerous ponds that the owners try to maintain them as Better Homes & Gardens swimming ponds. It can be tricky management especially when trying to keep the bottom sediments and gravel / sand from becomming anoxic, black, and smelly. That is a real challenge for most people and fairly difficult.
Depending on the cleanliness you expect, maybe rethink what you are doing and go with a standard pool. It is very difficult to maintain a natural earth bottom pond for the long term with pool like conditions. Mother nature ALWAYS wants to put natural things into the pond; numerous plants for one. Often unwanted ones. Many bugs and critters for two. Some of those bugs can be pretty nasty biters of unsuspecting swimmers. I always suggest a few (8-12) bass only for smaller (0.1-0.2ac) swimming ponds. They never bite swimmers and keep the bugs and nuisance invertebrates to a minimum and allow for proper zooplankton to thrive and promote clearer water.
Note the amount of plant biomass that is suggested in the above link. When all that plant material dies at the end of the year (winter) what happens to all that gunk/muck? If you or a filter has to remove it that is a daunting task in cool fall conditions.
Another concern - the side slopes. The above link suggests a 3:1 slope, which I agree with. Shallow water is the enemy of swimming ponds due to light always reaching the bottom and plants usually FA and slime constantly wanting to grow there. For 3:1 slopes and a depth of 8 ft the pond has to be at least 48 ft wide plus probably 8-10ft for a bulldozer to create a flat area in the belly of the pond which means 58-60 ft wide / long. Ideally the bottom of the pond should not be a V due to several reasons I will not take time to discuss here.
I disagree with some of the suggested plants for a pool pond in the above link (Elodea, hornwort, & duckweed). They tend to be rampant and cause too many problems for a lower maintence clear water pond. Hornwort can be okay but expect to annually harvest a lot of it out as it grows rampantly.
