Jumping into caffeinated water: The effect of caffeine on aquatic life

Photo credit

Written by: Rosie Caldwell

Human consumption of caffeine could be putting aquatic life under stress 3, 4, 5. Although most people think of pollutants as industrial chemicals, any chemical that isn’t supposed to be in the water is a marine pollutant and is likely to threaten ecosystems 5. New Zealand has been ranked the 13th largest consumer of coffee worldwide, even more than Australia and the USA. Each week Kiwis drink on average 2.5 cups of coffee 1 .

Caffeine is one of the most widely consumed legal drugs 3, 2. It affects our brain function which causes change in our behaviour, mood, cognition and consciousness 6. Caffeine is found in many commonly consumed drinks, food and pharmaceuticals 3, 5.Three percent of our intake of caffeine is passed out through our urine unchanged which means it ends up in waterways 3 . Caffeine affects aquatic life in a similar way to us, by increasing heart rate and activity 3 . This might be what we need to get us through a long day but for a fish this can cause unnecessary stress 2.

Sewage entering waterways. Photo credit.

Due to the growing cafe culture worldwide, caffeine is one of the most abundant and persistent compounds in surface waters 3 . A study in 2011 by Rey, Granek and Buckley on intertidal mussels showed that even low levels of caffeine caused native mussels to respond by releasing an increased amount of stress hormones 7 . On the other hand, some studies suggest that the level of caffeine detected in waterways is not a serious threat to the health of aquatic life 3. This could be true. But, caffeine is still used to track the movement of sewage in the ocean containing other harmful human contaminants, such as personal care products, hormones and detergents 2 .

I realise this is a sensitive subject for the world’s many caffeine consumers – do we really need to feel guilty for enjoying that indulgent cuppa that has become an integral part of our culture? People’s love for coffee seems to have begun in the fifteenth century when coffee shops and consumption started increasing 6. Then in the seventeenth century coffee became one of the earliest global commodities. In 2015, the International Coffee Organisation (ICO) predicted that the world produced nearly 19 billion pounds of coffee or 606 billion 6-oz cups 6. That’s a lot of caffeine going down the toilet and into our waterways! 

Products containing caffeine. Photo credit.

To understand the full environmental impact of caffeine on aquatic life, more research needs to be done. Aquatic ecosystems are sensitive to subtle changes in water quality. Studies have shown that even the usually sluggish and laidback bottom feeders become more active when exposed to caffeine 2 . Sources of human contamination need to be identified and reduced to protect the aquatic environment. There also needs to be more awareness and studies so that we can better understand the impact of contaminants like caffeine on aquatic organisms.

So next time you reach for your daily coffee, remember it’s not just affecting you.


  1. The Register team. (2017, May 2). Canstar Blue Survey results: We’re obsessed with coffee. The Register Retail Intelligence. Retrieved from https://theregister.co.nz/news/2017/05/canstar-blue-survey-results-were-obsessed-coffee
  2. Besant, A. (2012, August 29). Caffeine being dumped in the ocean is making fish nervous. Global Post. Retrievd from https://www.pri.org/stories/2012-08-29/caffeine-being-dumped-pacific-making-fish-nervous
  3. Capolupo, M., Valbonesi, P., Kiwan, A., Buratti, S., Franzellitti, S., & Fabbri, E. (2016). Use of an integrated biomarker-based strategy to evaluate physiological stress responses induced by environmental concentrations of caffeine in the Mediterranean mussel Mytilus galloprovincialis. Science of the Total Environment, 563, 538-548.
  4. Cruz, D., Almeida, Â., Calisto, V., Esteves, V. I., Schneider, R. J., Wrona, F. J., … & Freitas, R. (2016). Caffeine impacts in the clam Ruditapes philippinarum: alterations on energy reserves, metabolic activity and oxidative stress biomarkers. Chemosphere, 160, 95-103.
  5. Staff Writer Natural Health News. (2012, July 23). Swimming in a sea of caffeine. Natural Health News. Retreived from https://www.naturalhealthnews.uk/environment/2012/07/swimming-in-a-sea-of-caffeine/?fbclid=IwAR2BWytf8K4PvTJ0LsB5xfkjfZgFGrnAN73WYxHq-G77L3-G7C6wl0qiSwc
  6. Tucker, C. M. (2017). Coffee culture: local experiences, global connections. Routledge.
  7. Del Rey, Z. R., Granek, E. F., & Buckley, B. A. (2011). Expression of HSP70 in Mytilus californianus following exposure to caffeine. Ecotoxicology, 20(4), 855.