Key takeaways
- Insect repellent does not stay on your skin. It rinses off when you swim, shower or do the laundry, and it travels onward into rivers, lakes and wastewater.
- DEET is one of the most frequently detected organic wastewater contaminants in US Geological Survey stream sampling — mostly because it is used in enormous volumes and is not fully removed by conventional treatment.
- Biodegradable means micro-organisms break a substance down into simple, harmless compounds. The useful question is always how fast, and under what conditions.
- Plant-derived actives such as PMD (para-menthane-3,8-diol) are close relatives of compounds that already occur in nature, so environmental microbes degrade them more readily.
- Your habits matter as much as your bottle: apply repellent away from open water, wash well back from the shoreline, and never tip greywater into a stream.
Most people choose an insect repellent by thinking about their skin. Very few think about where it goes afterwards — yet a summer of swimming, showering and washing sends a measurable amount of repellent into rivers, lakes and the wastewater system. This guide explains how repellent reaches open water, what biodegradable actually means in laboratory terms, and what genuinely reduces the footprint of protecting yourself from mosquitoes and ticks.
How does insect repellent end up in rivers and lakes?
Repellent is designed to sit on the surface of skin and clothing, which is exactly why it comes off so easily. Every route below is ordinary, everyday behaviour — none of it is misuse.
| Pathway | What happens | What reduces it |
|---|---|---|
| Swimming and paddling | Repellent on skin washes directly into open water within minutes of entering a lake or river | Apply 20–30 minutes before you go out; do not top up immediately before a swim |
| Showering at home | Rinse water goes to a treatment plant; compounds that resist treatment pass through into the receiving river | Choose actives that break down readily rather than persisting |
| Washing while camping | Greywater poured on the ground or into a stream skips treatment entirely | Wash at least 30 metres from any watercourse; scatter greywater on soil, never into water |
| Laundry | Treated clothing and towels shed residues into wash water | Treat only the clothing you actually need to treat |
| Packaging and production | Bottles, propellants and manufacturing carry their own footprint | Plant-based or recycled packaging, larger sizes, fewer single-use formats |
Two of these are worth pausing on. Wild swimming puts repellent into water that has no treatment step at all — the lake is the endpoint. And treated wastewater is not filtered water: plants are built to remove solids, nutrients and biodegradable organic matter, not every synthetic molecule that reaches them. Whatever resists that process continues downstream.
What does biodegradable actually mean?
Biodegradable is one of the most loosely used words in consumer marketing, so it helps to know what it means to a laboratory. In standardised testing, a substance is placed in water with a community of micro-organisms, and testers measure how much of it is mineralised — broken down into carbon dioxide, water and biomass — within a fixed window, usually 28 days. Substances that pass that threshold are called readily biodegradable. Substances that do not are described as persistent, which simply means they stay intact in the environment for a long time.
- Biodegradable — micro-organisms can break it down. On its own this says nothing about speed.
- Readily biodegradable — the large majority breaks down within roughly a month under standard test conditions. This is the meaningful claim.
- Persistent — resists breakdown, so it accumulates in water and sediment as more is added.
- Bioaccumulative — builds up in the tissue of organisms faster than they can excrete it.
Persistence is the property that matters most for a river. A substance that degrades in weeks arrives, breaks down and is gone. A substance that resists degradation is topped up faster than it disappears every summer, which is how low-level contamination becomes permanent contamination.
Why DEET keeps turning up in water monitoring
DEET is effective, and it is recommended by the CDC, ECDC and the US Environmental Protection Agency for protection against mosquitoes and ticks. It is also, consistently, one of the compounds most often detected in surface water. A landmark US Geological Survey reconnaissance of American streams found DEET among the most frequently detected organic wastewater contaminants, and it has remained a standard marker in emerging-contaminant monitoring ever since.
Detection is not the same as damage, and it is worth being precise about that. What repeated detection does tell us is that DEET is used at enormous scale, that it survives the journey through wastewater treatment, and that it therefore reaches rivers more or less continuously through the summer. That is a footprint question rather than a toxicity headline — but it is a real one, and it is the reason we made the choice we describe in why we are DEET-free.
Where plant-based actives differ
The active ingredient in incognito® repellents is PMD (para-menthane-3,8-diol), sold under the trade name Citrepel®. In our formulation it is derived from Cymbopogon winterianus, Java citronella. PMD is not a soft alternative to a serious repellent: it is the same class of active that the CDC and ECDC list alongside DEET and picaridin for protection against mosquitoes and ticks, and a peer-reviewed review in the Malaria Journal concluded that PMD-based repellents give protection comparable to DEET at lower concentrations.
The environmental argument is structural rather than promotional. PMD is a close relative of terpenoid compounds that plants already release into their surroundings, so soil and water microbes have existing enzymatic routes to degrade it. Our formulations are biodegradable and vegan, and the bottles are made from sugarcane-derived plastic — the same logic we apply to sun care, where the ingredient choice reaches the water directly, as we covered in our guide to reef-safe sunscreen.
Six habits that keep rivers and lakes cleaner
- Apply repellent 20–30 minutes before you head out, so it binds to skin rather than rinsing straight off in the water.
- Cover the skin that is actually exposed. More product on more skin is not more protection — it is more runoff.
- Do not reapply immediately before swimming. Reapply after you come out and have dried off.
- When camping, carry water at least 30 metres from the shoreline to wash, and scatter the greywater on soil where it can filter through.
- Use a biodegradable body wash for washing outdoors, and skip washing altogether on short trips where it is not needed.
- Buy the size you will finish, and prefer refillable or plant-based packaging over single-use formats.
How incognito® helps
We built the range around the idea that protection and biodegradability are not a trade-off. Our Insect Repellent Spray is DEET-free, clinically proven, vegan and biodegradable, and it is recommended against both mosquitoes and ticks. The wider incognito® range follows the same rules — plant-based actives, sugarcane packaging, and formulations made in the UK. In 2026 the company received the King’s Award for Enterprise for Sustainable Development, which is the part of this we are proudest of.
FAQs
Is insect repellent bad for lakes and rivers?
Any repellent that washes off enters the water, so the honest answer depends on the ingredient and the volume. Persistent synthetic actives accumulate because they are added faster than they degrade; readily biodegradable plant-based actives break down within weeks.
Does DEET break down in water?
It degrades slowly enough that it survives conventional wastewater treatment, which is why it is among the compounds most frequently detected in stream monitoring by the US Geological Survey.
Can I swim with insect repellent on?
Yes, but most of it will wash off, which is bad for both your protection and the water. Apply well before you go out, and reapply after swimming rather than before.
What does biodegradable mean on a repellent bottle?
It means micro-organisms can break the formulation down into simple compounds. The stronger version of the claim is readily biodegradable, meaning the large majority breaks down within about 28 days in standard testing.
Is a biodegradable repellent less effective against ticks?
No. PMD is one of the actives recommended by the CDC and ECDC against mosquitoes and ticks, and published reviews report protection comparable to DEET at lower concentrations.
Where should I wash when camping near a river?
At least 30 metres from the water, using a biodegradable wash, and scatter the used water on soil so it filters through the ground rather than running straight into the stream.
Sources
- US Geological Survey — Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams
- US Geological Survey — Emerging Contaminants
- US Environmental Protection Agency — DEET
- US Environmental Protection Agency — Skin-Applied Repellent Ingredients
- CDC — Preventing Mosquito Bites
- ECDC — Protective measures against mosquitoes
- European Environment Agency — Europe’s state of water 2024
- Maia & Moore, Malaria Journal — Plant-based insect repellents: a review
- NHS — Insect bites and stings
This article is for general information only and is not medical advice. Always follow the instructions and age guidance on the product label, and speak to a pharmacist or doctor if you have questions about a bite, a rash or a specific health condition.