Natural Indicators of Water Pollution

In my front yard/cow pasture, there is a creek, my favorite spot to go iNatting. There are tons of insects, lovely wildflowers, fish and crayfish galore, damselflies in abundance–and my mom says I should not touch the water because there’s probably a lot of glyphosate in it, which can cause cancer.
So, there’s a lot of conventional farming being done in my area, lots of glyphosate and insecticide being spraying on the corn and soybeans. I know that these sprays will run off into the water supply. But, if there was a lot of glyphosate, wouldn’t there not be as many plants? And if there was insecticide, wouldn’t the insects be not as abundant? And what about the fish and crayfish, that live in the possibly polluted water? Are there any natural signs of water poisoning? (And I mean on the observable scale, with non-microscopic organisms.)
Thank you all in advance!


As with any poison, the concentration matters. It may be that the concentration of these pesticides and herbicides in the water is too low to cause mortality in the fauna you’re observing there, but even a less-than-lethal dose can have chronic health effects over time. Your fish and crayfish and insects do not live long enough naturally for chronic exposure to be a concern, but for a human who lives much longer, regular exposure to small doses can cause problems like cancer depending on which toxins are present.

Additionally, it’s likely that the concentrations that you could be exposed to are not constant. Glyphosate in particular binds strongly to soils and organic matter, so it could be that on a normal day, the concentration in the water is relatively low. On another day, for example after a heavy rain that stirs up sediment in the water or in the days immediately after farmers upstream spray their crops, the concentration of contaminants in the water could be much higher and pose a greater risk. If there is herbicide and pesticide runoff into your stream and the water is not regularly tested, then your mother is right to be cautious.


There are certain species that can only be found in non-polluted water, and some that are more hardy and can be found in polluted water (like Rat-tailed Maggots). I don’t have a list, but if you look into this and keep an eye out for those organisms, it can be telling. I learned about this in a toxicology course. I can try to find my notes if you’d like.


But crayfish are very sensitive to pollution, wouldn’t it affect them anyway?


I wouldn’t worry about glyphosate, personally, or even the insecticides. As for your questions about visible impacts: The former has to enter though leaves to effect roots, so wouldn’t necessarily kill plants even if present. The latter would be expected to reduce insect populations if relevant concentrations.

What you might want to worry about are toxic bacteria. These can come from fertilizer, elevated temperatures from sediment and loss of shade, and directly from waste.

In terms of studying water quality using biology, the gold standard (as I understand it) is to look at benthic macroinvertebrates (bottom-dwelling large insects). cf here:


As far as signs, it’s hard to say. Sometimes you’ll see obvious things like fish kills, but some things leave no readily-observed signs whatsoever. The most common biological assessment is macroinvertebrate sampling.

Maybe that could be your next iNat adventure. Get yourself a net, a couple jars and a pair of waders. If you like it, maybe you decide to do a larger project. Sample several water bodies, compare upstream vs downstream, or samples taken before vs after spraying. Maybe that becomes a scholarship opportunity or something. In PA, we have PJAS, for young scientists. Maybe your state has something similar:

Doing a google scholar search for something like “aquatic macroinvertebrate water quality insert-your-state/region-here” should give you a path to find a good study design as well as studies to compare your results to, to see how polluted your stream really is. If you’ve never read peer-reviewed articles before, it can be tough at first, but there’s a lot to learn from them, so it’s worth it.

There’s youtube, too:

I’m sure there are people in the forums who could give better guidance than me, too, if you ask about sampling techniques and study design. I’m mostly a wildlife/tree guy.

Otherwise, the word “pollution” encompasses a lot of things. For example, I can almost guarantee that the biggest pollution in your area is actually nitrogen runoff from fertilizers and manure. What would the signs of that be? Lush, green plant/algae growth (and maybe a fish kill if levels are extremely high), which isn’t the first thing that comes to mind when most people think of pollutants.

Something else to be aware of is the chemistry of different pollutant compounds. What is the compound’s half life? Does it bind chemically to compounds in the soil? Is it metabolized by by microbes? Is it destroyed by UV radiation from the sun? Does it bioaccumulate and/or biomagnify? Does it behave differently in water vs surrounded by air in a terrestrial environment? Is it water-soluble?

For example, glyphosate has an average half life of 90 days, that can range between 3 days and 19 weeks, depending on environmental conditions. I’ll bet that most of the compounds that enter the water are washed away or get destroyed pretty quickly, unless they bioaccumulate like PCBs or mercury.

Overall, I wouldn’t be freaking out if I got wet from a moving creek in your area, I’d just be sure to shower afterward. But I wouldn’t be walking through fields unless I knew for sure they hadn’t been sprayed in several months, and I wouldn’t be outdoors when I know they’re actively spraying.


They are also sensitive to low oxygen from an algal bloom

There may be small amounts of glyphosate in your water, but why would it also not be in the soil? And in the air that enters your house (it’s applied as a spray)? At very high doses it may increase risk of cancer (although the evidence is weak), but not at doses most humans encounter except those who drink it or bath in it. And yes, if the creek contained high concentrations of glyphosate, it would cause some harm to some living organisms (plants and algae mainly). But we’re talking gallons being poured into the creek daily–not overspray from fields.


I would not worry seriously about glyphosate in the creek water unless you know specifically that large quantities are being dumped or something. Glyphosate has a high half-life in soil, but not in water which will also dilute it. Absorption across skin isn’t that high (you’re not drinking the creek water in volume). Toxicity to humans is pretty low.

I agree that other pollutants like bacteria are a greater concern in a creek.

Doing most things in the world involves some small amount of risk. In fact, the riskiest thing most people do on a daily basis is drive somewhere in a car, but we still drive all the time (in the US anyways), so I would advocate for not letting very small risks stop you from doing something that you’re really enthusiastic about.

Another angle is that exercising via stomping about in the creek is good for your physical health, and being out in nature is good for your mental health. These benefits would almost certainly outweigh the very small risk of glyphosate exposure from creek water.


Thank you all for the replies! I’m not going to worry seriously about the glyphosate in the creek. It seems like a pretty stable ecosystem there.

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Possibly, but given there’s a known contamination source nearby, without knowing what’s in the water and at what concentration I wouldn’t take unnecessary risks. We also don’t know for certain that there isn’t any aquatic mortality in the creek. It doesn’t necessarily mean it presents some immediate danger, but limiting exposure couldn’t hurt. Nor would testing a sample.

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Hey there

It’s great that you have a little wetland to explore and look for small organisms and plant life, one of the sublime joys of living in the countryside! By what you describe in your post, it sounds like you are surrounded by commercial crop farming. If that is the case, then its more than likely that Glyphosate is present in some kind of quantity in the soil or water that you tread around, seeing as the U.S FDA has yet to regulate the use of glyphosate-based herbicides in any State

Despite what a few have said here, you certainly SHOULD be cautious about exposure to glyphosates, through skin contact or vapour inhalation. The scientific consensus on the harms this can cause to human health is abundantly clear and pretty much beyond debate, despite what companies like Bayer would have you believe. Glyphosate usage in my native country of South Africa is also not regulated at all, and if you walk into any one of our agri-suppliers or even hardware shops, RoundUp is freely available on the shelves

The older glyphosate compounds use to bind very closely to soil after being sprayed, and even using accurate targeting techniques, the fauna in and above the soil would suffer greatly from related poisoning which would accumulate up the food chain. These days, there are newer phenyl-based derivatives of Glyphosate which do not readily stick to surface debris or soil but tend to sink down into substrates and get swept away with runoff water. They dissolve more easily in water though so the trade-off is that these newer glyphosates pose a risk to aquatic fauna. I’m guilty of using glyphosate based products to eradicate really aggressive alien vegetation some years ago, the only thing that free’s me from feeling guilty is that I did this in the middle of our dry season (June) where we get almost no rainfall. By the time the rains did come, most of the harmful components of that herbicide would already be inert

If you spray this just before heavy rains though, and it gets into drainage lines and eventually streams and rivers, you will have big problems on your hands!


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