salt and/or chlorine can wipe out a nearby stream fairly quickly and easily. even if the stream only runs a couple times a year.
streams / lakes / ponds. are not artificial things, they do have there own eco system going on with them. and it does take time for stuff to grow back.. bacteria, single cell organisms, algae, etc.. between on a well, and septic system, a stream on the farm, a couple lakes, plus couple thousand gallon pond down stairs.... have had to learn the hard things, the hard way. (falling flat on face)
contact local water department / city sewers or what not. as others have said it differs every were. some locations charge for incoming water (drinking water), along with (sewage water) and pools are extra costs / fees.
some require water to be trucked in and out.
some places you can dump water but you need to be X feet away from a body of water (stream, lake, pond, etc.. even if water is only there a couple times a year) the X feet, is more about letting the water slowly trickle through the grass / ground, and get filtered out, before it reaches the given body of water.... other words instead of a slow trickle out of the water faucet, ya end up opening a 2" hose powered by a 3HP pump... large difference in GPM. from say 50 gallons an hour to a few thousand gallons per hour... slower is better. and if dumping a huge amount of water, say from a swimming pool. then dump a couple hundred gallons, give it a few hours, dump another couple hundred gallons, etc... all the water to soak in and filter itself as it flows to a given body of water. you may need to wait a day or two between amount you dump.
all systems can take the water, it just depends on how much and how quickly it can handle it. before ya destroy stuff (killing grass, algae, fish, etc...), slower and less amount at a time always better. but generally when ya get to about this for a common person, it is about time ya talked to an engineer familiar with what to do, in the given situation.