A reality check on barriers

Members of the AMBER project have this week responded to an earlier article in Nature which reported disruption via dam construction of two-thirds of large rivers worldwide. They use their comprehensive assessment of stream fragmentation in Great Britain to highlight the role of small dams too: 97% of the GB river network is fragmented and <1% of catchments are free from artificial barriers of some sort…shocking stats! Across Europe, some 415000 barriers have so far been identified (mostly small in size but not in impact). We at WTT contribute to the reporting of barriers, as well as advising upon solutions and, in some cases, actually securing funding and dealing with the issues associated with dams directly (eg on the Dove or Aire), as followers of the blog and readers of our newsletters will be aware. 

Graphical abstract lifted from the AMBER paper (in the journal, Science of the Total Environment)

Fishy folk on social media must surely have come across Kim Birnie-Gauvin (@kbg_conserv), part of the AMBER project, PhD candidate at DTU Aqua in Denmark, ambassador for World Fish Migration Day, amongst many other things! She’s just launched her new website — check it out: www​.kbg​con​serv​.com

Here, Kim gives us a few thoughts as a brief reality check on barriers…. 

Barriers have devastating effects on fish and the environment they rely on. Some fish populations have gone extinct following the construction of dams (e.g., Welcomme 1985; Wei et al. 1997; Jepsen et al. 1998; Morita and Yamamoto 2002), yet the belief that hydropower is a green’ energy remains firmly grounded in our society. If the question is whether hydropower is better for the atmosphere than burning coal, then yes, perhaps hydropower is greener’ although there are some worrying statistics regarding the amount of greenhouse gases like methane that are generated by damming of rivers which seriously offset and negate their green’ credentials. But just how green’ should hydropower be considered if it has caused the extinction of fish populations around the world? Should it be considered green’ if we know that a large proportion of endangered eels facing hydropower turbines won’t survive?

Marble Bluff Dam fishway (photo credit: Todd Plain)

In an attempt to make barriers more transparent and to mitigate the passage issues, we – humans – have developed fishways. These come in the form of fish ladders, fish elevators and so on, but ultimately they are engineered solutions that prolong an existing problem. Barriers cause many more issues that fishways cannot address, including the destruction of suitable habitat, physical injuries and predation associated with impoundments (highlighted in my recent paper; Birnie-Gauvin et al. 2017). The expression fish-friendly’ has been developed and used to describe improved turbines, but how can that be? Just because a turbine is perhaps less deadly does not make it friendly. This wording is misleading.

Conservation goals set by governmental agencies are also misleading, with competing requirements from two sectors whose agencies don’t communicate, but whose fields overlap. On one side, the European Union requires its environmental managers to protect and enhance all artificial and heavily modified bodies of water”; on the other, it encourages its energy industry to build small hydropower dams, which will inevitably create more heavily modified water bodies. 

Barrier removal is the only green’, fish-friendly’, non-misleading option to reinstate natural conditions. Removal reinstates suitable habitat, provides free access for fish migrating up- and downstream without causing delays, and so on. When removal is not an option, and this should only be the case for very large rivers with multiple dams already in place, then an adequate, well-designed fishway should be constructed to allow all species through. Despite every effort, we know that not all individuals will make it through, and some will inevitably get delayed or die. For that reason, conservation efforts should also be applied elsewhere within the system to alleviate the inevitable consequences of the barrier by for example restoring parts of the river that the fish will have access to. An additional requirement should be for each country to have a set percentage of watersheds completely free-flowing (i.e., no barriers).

The small hydropower industry was expanding at 1500% per year according to a study a couple of years ago (Zarfl et al. 2014). Plans to fragment some of the most diverse watersheds in the world (the Mekong, Amazon and Congo Rivers) are continuously growing (Winemiller et al. 2016). Some undiscovered species are likely to go extinct before they are discovered! Our rivers need us, and they need us now.

Yecla Dam, Spain (image from Dam Removal Europe)

In their Nature correspondence last year, Ali and Xie proposed that Pakistan needs more reservoirs, and fast”. They stated that the sixth largest population in the world is in dire need of more reservoirs to maintain water security, arguing that climate change will lead to massive droughts and that the current government has yet to build a dam large enough to sustain its population’s growing demand.

Here’s why I think the world needs less reservoirs, and fast.

Worldwide, more than one third of all freshwater species are threatened. Reservoirs are responsible for a great majority of these. They ruin habitats suitable for some of the world’s most iconic species, on which nearly 158 million people depend just for food. So why build a dam to ensure water supplies if you extirpate all that lives within? 

The argument that climate change will dry rivers is severely outweighed by the increasing water demands for human’ consumption (Vörösmarty et al. 2000), which goes primarily toward industries. We would urge that governments should sanction industries on their water use before considering species extinction as a viable option. The Pakistani government’s indecision in allowing dam construction should be applauded.

Freshwater ecosystems are the most endangered of all ecosystems. Reservoirs are paving the way for a serious biodiversity crisis (Winemiller et al. 2016). I beg global practitioners to acknowledge the truth about these deadly man-made structures before it is too late. Let’s be real.


Ali, T., & Xie, W. (2018). Why Pakistan needs more reservoirs, and fast. Nature, 560, 431,

Birnie-Gauvin, K., Aarestrup, K., Riis, T.M.O., Jepsen, N., & Koed, A. (2017). Shining a light on the loss of rheophilic fish habitat in lowland rivers as a forgotten consequence of barriers, and its implications for management. Aquatic Conservation: Marine and Freshwater Ecosystems, 27, 1345 – 1349.

Jepsen, N., Aarestrup, K., Økland, F., & Rasmussen, G. (1998). Survival of radiotagged Atlantic salmon (Salmo salar L.) – and trout (Salmo trutta L.) smolts passing a reservoir during seaward migration. Hydrobiologia, 371, 347 – 353.

Morita, K., & Yamamoto, S. (2002). Effects of Habitat Fragmentation by Damming on the Persistence of Stream-Dwelling Charr Populations. Conservation Biology, 16, 1318 – 1323.

Vörösmarty, C. J., Green, P., Salisbury, J., & Lammers, R. B. (2000). Global water resources: vulnerability from climate change and population growth. Science, 289, 284 – 288.

Wei, Q., Ke, F., Zhang, J., Zhuang, P., Lou, J., Zhou, R., & Wang, W. (1997). Biology, fisheries, and conservation of freshwater biodiversity 181 sturgeons and paddlefish in China. Environmental Biology of Fishes, 48, 241 – 255.

Welcomme, R.L. (1985). River fisheries. FAO Fisheries Technical Paper (262), pp 30.

Winemiller, K. O., McIntyre, P. B., Castello, L., Fluet-Chouinard, E., Giarrizzo, T., Nam, S., … Sáenz, L. (2016). Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong. Science, 351, 128 – 129.

Zarfl, C., Lumsdon, A. E., Berlekamp, J., Tydecks, L., & Tockner, K. (2015). A global boom in hydropower dam construction. Aquatic Sciences, 77, 161 – 170.