We have a 100' across spring fed (it's a trickle but keeps it full) pond in our front pasture. It has alternated between gorgeous and muddy, depending on the weather. The last few weeks, it has had a stagnant look to it, with a lot of pollen/dirt/whatever floating on top. It smells fine (we were worrying that someone's septic tank was leaking or something like that, since this hadn't happened in our two years here). Does anyone use a bubbler or anything like that in a farm type, versus ornamental type, pond? When they are in this pasture, the horses drink from the pond. It looks better today, because we had a nice rain (finally) last night, but I'm assuming it will be back to yucky in a day or two. Normally, the kids swim in it, the dogs play in it, and it is the horses' source of water.
The mud is just run-off from the pasture. When we've had rain, it has been hard and heavy.
I asked my county agent and at Co-op about testing the water, but they both said that it is such a moment in time result (because the pond is constantly changing) that there wasn't much point. We have fish, turtles and 8 zillion frogs. My county agent said that as long as we have lots of healthy frogs, the water is healthy, because frogs are so sensitive to toxicity.
I wouldn't let the kids swim in it. There is some sort of parasite that gets in warm still water. If it gets into a human system, it goes to the brain and is fatal. I have kept our pond fairly fresh by simply running water from the hose into the pond.