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I love the outdoors, but I'm not really an experienced outdoorsman, hiker or camper. I have little to no education in outdoor etiquette, beyond the really obvious stuff (pick up your trash, etc.).

Last week I took my family on a road trip through a mountainous area, and we stopped at several little mountain streams and waterfalls to explore the area and enjoy the view. On many of these trails, my young toddler had a great time picking up dozens of pebbles and small stones from the path and throwing them into the stream / waterfall / pond / etc.

Only later I thought to wonder if there's something wrong with doing that. Were we contributing to erosion, disturbing animal habitats, interfering with water courses, or something? Should I stop him from throwing rocks in the future and educate him about why that's not environmentally conscious, or is it not a problem, so I can let him throw pebbles to his heart's content?

(My personal guess is that driving our car through the area [on public roads] probably did more environmental damage overall than throwing a few pebbles, but, well, I really don't have any education to back that up!)

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    Interesting question, I've spent the past 30 years skimming stones and never thought about this. – Aravona Jun 28 at 13:33
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    Certainly one should not let anyone throw stones off cliff edges, or anywhere else that there might be somebody below and out of sight! – Jon Custer Jun 28 at 13:52
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    This seems like a great chance to teach him (in a basic way) about the nuances of human impact and recreation in the wild. You can let him keep throwing pebbles in the stream (fun!) while explaining what not to do (throw rocks off cliffs, move very large rocks, take rocks home). It's the same tension between use and preservation that we all face in the outdoors--what a wonderful and easy way to introduce him. – jhch Jun 28 at 18:57
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    This is a great question! It's wonderful that you care enough to be concerned. Moving rocks, even little ones, in, out or around their natural habitat is dangerous for eco-systems. In some USA National Parks, including Great Smoky Mountains National Park, it's even illegal to move rocks. Getting your son excited about the environment can never start too young. You guys can have a great time doing it together and he might grow up to make a huge difference in the world! – Sue Jun 29 at 3:25
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    Whatever your clearly good motivations are, please don't spoil throwing pebbles into all kinds of waters for your toddler! – imsodin Jun 30 at 16:11
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Technically, according to Leave No Trace principles you should leave everything as you find it. Two other related principles would be travel on durable surfaces and respect wildlife. As you intimated, fewer rocks on the trail could perhaps make it less durable and more susceptible to erosion. Obviously throwing rocks directly at an animal (unless for protection) would not be respectful, but I don't know if the underwater life gets agitated or negatively affected in some way by rocks hitting the surface and sinking to the bottom.

Would I stop my child from throwing a few rocks in a lake or stream? Not normally. If I thought it was excessive, I'd get after him and explain why.

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    Your closing statement clearly shows that you got this point, but opening with "Leave No Trace" for a toddler throwing pebbles is just so disproportionate. This proves that you can drive the best idea ad absurdum if you ignore that it may be formulated in absolute terms, but that it can't be absolute and is meant as a guiding principle. – imsodin Jun 30 at 16:18
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    @imsodin I'm confused. To me, the answer says that Leave No Trace is the ideal, then looks at why we want to leave no trace and concludes that throwing a few stones is Leave Not Much Of A Trace so is probably OK. And that seems to be exactly what you're advocating. – David Richerby Jun 30 at 16:34
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    @DavidRicherby I didn't interpret it that way: To me it seems it says you shouldn't do it, but still not prevent the toddler unless excessive. I guess what prompted my reaction was mostly that I just recently witnessed yet another really bad case of casual littering, and in general there's so much so really, really bad behaviour in terms of leave no trace, so I think it's wrong to make people that already are aware of it to it feel bad about minuscule aspects, let alone totally insignificant ones like this. – imsodin Jun 30 at 16:49
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    You can't go hiking without leaving a trace. So the objective is to minimize the trace, but this leaves too much wiggle room, so we say "leave no trace". Would a hiker leave less trace if he never hiked? Depends of course on what he did instead. Someone's probably written her PhD thesis on this. As for the toddler, let him have fun and learn to love the outdoors. – ab2 Jun 30 at 22:29
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    @imsodin That is why I opened with "Technically". To me at least this question isn't as absolute as littering, which I would be totally against at any age. My boys and I frequently pick up other's trash on our backpack trips. Generally, we do follow leave it like you found it. If we clear a site of debris to camp, we spread it back when we're done. But I still skip the occasional stone across a lake. ;) – topshot Jul 1 at 12:45
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Nature is not static, it is always in motion.

Let's look at two extremes.

A small pothole full of water on the trail can be completely filled with a couple of handfuls of gravel. Expand this to a small pond at a park and have daily visitors tossing gravel from the path in to the pond, and soon the pond is gone (the path will need fresh gravel as well). In any case, a pond exists because moving water encounters a depression, the water slows and deposits sediments, these sediments eventually fill the depression, and in a few tens to thousands of years the pond is gone.

Niagara Falls is a large waterfall, the erosion is significant, and if a few visitors a day toss a pebble from the path into the falls, the impact is negligible. In another 23,000 years the falls will be gone.

Niagara Falls has moved back seven miles in 12,500 years and may be the fastest moving waterfalls in the world. Source

While there are no absolutes, in general throwing things in still water like ponds and lakes is going to have a more significant impact than nature might have by herself. Tossing a round stone from a river bank into quickly moving water is less of an environmental impact: in all likelihood, the river deposited the rock on the bank, and it has been in and out of the river flow several times.

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    Yeah, throwing rocks in is not just "okay," it's part of enjoying nature. Those rocks will be in the stream in a short time, anyway. Not only that, worrying about the contribution to erosion is like asking if turning on a flashlight makes the day too bright. – Don Branson Jun 29 at 20:29
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    For the Niagara Falls, a significant portion of the water is now diverted away from the falls, so it is actually moving back much slower than it would naturally. :) – vsz Jul 1 at 5:20
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In addition to the other answers here, I would point out that the trail itself may be maintained using a light application of gravel to prevent erosion or excessive runoff.

Removing pebbles from the trail could, over time, degrade the trail itself. I doubt it was a very big deal for your toddler to throw a few pebbles, but if everyone who visited the trail threw a few the trail might be damaged quite quickly. So gently educating your toddler to respect the work of the people who maintain the trail might be the best way to go.

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Some places have rocks on the shore that arrive there naturally. The effect of a few dozen people per mile people picking up a rock from random locations uniformly distributed along a moving river would be trivial compared with the motion of rocks in and out of the water from natural causes.

A point that hasn't been mentioned, thouh, is that other places have rocks manually placed on them to help control erosion. The more of these rocks get tossed in the river, the more effort someone will have to spend replacing them.

If people picked up rocks from uniformly-distributed random locations, the overall impact in either case would probably be fairly slight. Unfortunately, areas that have rocks manually added to control erosion tend to be more attractive to people wishing to skip stones than the areas which don't.

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    While I agree that manually placed rocks placed for erosion control are an important part of humans attempts at managing rivers, if they are small enough to be tossed, they are not effective at managing erosion. – James Jenkins Jul 1 at 15:34
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    @JamesJenkins: That would depend upon the movement patterns of the water in question. If the rocks are usually above water as at my parents' lake house, replacing the amount of rock that gets washed away in times of high water may be easier than replacing the amount of dirt that would have gotten washed away if the rocks weren't there. – supercat Jul 1 at 16:29
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Some places are more sensitive than others.

It can be hard to tell whether some innocuous-looking pebbles are a critical habitat for creatures you don't see, but a good guide is to look at how much natural movement of material there is.

The side of a fast-moving stream (even one that's dry right now but frequently floods) or a strongly tidal coast is subject to a lot more movement of rocks than us puny humans can manage unaided. They are great places to take your youngster for this kind of play¹, and wildlife that's disturbed can be assumed to be robust enough to tolerate it.

On the other hand, many still-water environments (even in man-made places such as old quarries) are more vulnerable to this kind of disruption and are probably best left alone unless you specifically know otherwise.


¹ I'm assuming that you have the safety aspect covered; that's not within the scope of this answer.

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I used to tell my children not to throw rocks in the ocean because eventually the ocean would get full and the earth would flood. Fortunately, they soon recognized that I was simply making a joke about logic. A toddler throwing stones in a stream? What is the nature of the setting? Is this an urban park or a wilderness setting? How likely is the behaviour to be repeated by others? If it is an urban park and the stones are on a gravel path then tossing those stones into the pond might best be discouraged. In a wilderness area? Throwing stones for a toddler is natural human-animal behaviour. Not only does it allow the toddler to develop skills in co-ordination, distance, and place which are critical skills and important for brain development especially in this time of google and 24-7 phones, but it also, and this is important, allows the toddler to develop a sense of belonging in the outdoors. A sense that they are good enough to be in nature. That they are equal in importance to the trees. That they exist not outside nature but within nature. A toddler throwing stones in a stream is completely different than a back hoe ripping into a stream. The difference is not just an order of magnitude. It is a completely different thing. To me it would make more sense to pick up a few stones and join the toddler in his or her pleasure at being outdoors than scold or lecture him or her about correct behaviour.

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