Is Roundup Weed Killer Safe To Use Near Water, Ponds, Or Lakes

Roundup is one of the most popular herbicides among home gardeners and professionals alike. While the Roundup brand consists of dozens of different formulas, the vast majority still rely on glyphosate as the primary weed-killing ingredient.

Despite what many people believe, glyphosate is not outright poison. But it’s certainly not safe in all contexts, either. In fact, the risk of glyphosate entering natural waterways is a heavily discussed topic in the world of agriculture and sustainability. 

Below I’ve explained everything that is currently known about whether Roundup weed killer is safe to use near water, as well as expert tips on how to use these products safely and responsibly at home.

Is Roundup Approved For Use Near Water

According to Oklahoma State University, Roundup products are not approved for use near natural bodies of water. It’s also not recommended to use them in or directly adjacent to unnatural bodies of water like fountains and swimming pools.

However, there are some aquatic herbicides that contain glyphosate, the same active ingredient as Roundup. It is worth noting here that it is not necessarily the glyphosate that is hazardous to bodies of water but rather other ingredients found in Roundup.

If you are searching for an herbicide that is safe for use around ponds, lakes, and more, you will need to select a product that is explicitly designed and labeled as such.

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Will Roundup Run Off Into Nearby Streams And Waterways?

The good news about Roundup and other glyphosate-based products is that they do not run off of the soil very easily. Because glyphosate binds tightly to soil particulars, it largely stays where it is applied until it breaks down.

With that said, there is still a risk of Roundup making its way into nearby streams, ponds, and other natural waterways. A common scenario where this is possible would be heavy rainfall shortly after Roundup is applied.

Is Roundup Safe Near Swimming Pools?

Roundup and other glyphosate-based herbicides are generally safe to use near swimming pools. While glyphosate can damage natural aquatic ecosystems, a small amount of the product won’t cause harm in a standard swimming pool.

It’s important to minimize the amount of herbicide that enters pool water, so I recommend spraying Roundup with a pool cover or tarp in place just to be safe. I also don’t suggest spraying Roundup near a swimming pool that is actively being used.

Though it should probably go without saying, you should not use Roundup near-natural swimming pools that contain aquatic plant life.

Is Roundup Safe To Use Near A Drinking Well?

Whether or not you should spray Roundup near a drinking well is a hotly debated topic. Some people opt to err on the side of caution and forego its use altogether, which is fine. 

With what we know about glyphosate and its impact on groundwater, however, well owners can still use Roundup as long as the following is true:

  • The well is functioning properly.
  • All herbicides are applied per their labels.
  • Excess glyphosate-based products are not dumped in or near the well.
  • Glyphosate is not sprayed within 100 feet of the wellhead.

Additional steps you can take to protect your well water are to install a filtration system and ensure the ground slopes away from your wellhead. Do not use Roundup prior to heavy rain or irrigation to prevent accidental run-off.

Will Roundup Kill Fish Or Aquatic Life?

It’s easy to forget how similar aquatic plants are to those growing on dry land. Aquatic plants exposed to sufficient glyphosate can be damaged or killed just like regular weeds. In most run-off cases, the glyphosate is diluted enough to not do much harm. But the risk is always there.

As for whether or not Roundup kills fish, the answer is not so simple. There is no evidence that direct exposure to glyphosate will kill fish outright. However, fish suffer greatly when Roundup kills aquatic plants and throws off the balance of their native ecosystems.

Does Roundup Kill Beneficial Aquatic Insects Or Flies?

According to a John Hopkins study, glyphosate may weaken the immune systems of some insects. This harmful side effect likely extends to aquatic insects as well. 

Keep in mind that some Roundup products are formulated with pesticides. Such products could do significant harm to aquatic insect populations following contamination.

Alternative Weed Killers Safe To Use Near Water

Just because glyphosate is relatively safe to use near the water does not mean it is the best option available. I’m a big proponent of treating Roundup and similar products as last resort in your weed-killing arsenal.

Weed management strategies like hand-pulling and smothering can be just as effective as chemical herbicides in the right context. While these methods take time and physical labor, they pose zero risk to nearby water sources.

I haven’t tried it myself but know of several gardeners who use distilled vinegar as an alternative weed spray. Just be aware that vinegar is non-selective and so can damage desired plants as well.

Verdict: Is Roundup Weed Killer Safe Near Water

If your garden contains an artificial pond, swimming pool, or fountain, it’s likely safe to continue using Roundup as directed. But you may want to look for water-safe alternatives if you live adjacent to a stream, lake, or other aquatic ecosystems that may be damaged by herbicide run-off.

Personally, I use Roundup in my own garden. However, I leave a wide margin of untreated ground around my ornamental pond to prevent contamination. It may not be a natural water source but there are still plenty of frogs, toads, and birds that visit it daily!