Fish-Tales (English)

'Onder water in Leiden' translates as Under water in Leiden.

NEWS! What's a Christmas tree doing in the canal?

  • An "artificial reef" has been placed in the Binnenvestgracht, beneath the bridge at the cemetery Groenesteeg. It was the old X-mas tree from the Beestenmarkt, kindly donated to us by De Bloemenboot.
  • It will knijpgrijper met ijsvogel_bewoners onderzoeken bewonersprovide shelter, food and ample space for native predatory fish to lay their eggs. Think: pike, zander, perch and sticklebacks.
  • The past years we noticed that invasive species like the roundhead and tubenosed gobies liked to eat their eggs, because they're the first protein-rich food source after the winter.
  • American Crayfish are decimating waterplants, therefore destroying sites for fish to cling their eggs on.
  • It's a trial to see if the pine tree will deter exotic species (results unknown), for native species to lay their eggs and hide in without being disturbed by gobies and crayfish (positive results expected).
  • It will last until June 2023 or even longer, if the results are satisfying. We'll be monitoring that closely!
  • We'll be picking up the floating trash next to the reef with our XXL graspers, fishing nets and if necessary our clean-up kajak. 
  • Here's the Dutch information leaflet about this project.
  • P.s. we're trying with council and owners to get the two licensed boats another location to moor their vessels. This will prevent any more oil-spills. 
  • The boat barrier/reef will also deter misinformed boats that wish to sail on through this part of the fish reservation (see below; Dutch only).

Recap of our project

  • 'Under water in Leiden' is a unique project in the Netherlands, started by locals in 2011. Locals became interested in the life under the surface after the city-canals got cleaner and clearer.
  • This clarity (and growing abundance of wildlife) was mainly due to well-planned maintenance of the waterways within the city and surrounding areas.
  • The project 'Monitoring of Fish', encompasses the checking and counting of wildlife in the canals and is since 2013 an official biodiversity project.
  • 26 species of fish have been spotted in Leiden, by trained volunteers and fishermen alike.

victoria wolhandkrab hoornblad
jun2019 10a schildpad geelbuik
onderwaterinleiden de-doorbraak schildpad nagellak
rivierdonderpad leiden danielsiepman
jul2017 10a toverstokje
onderwaterinleiden pike city-canal sunlight
onderwaterinleiden meerkoet dood-snoekje
groep-karpers whalewatching

Support from local and nationwide institutions

  • Under water in Leiden is supported by the Leiden council, various institutions who work with and on the waterways and of course widely appreciated and cared for by the locals.
  • Almost 50% of the monitoring is done snorkelling in the canals, with a special permit, since swimming in the canals in Leiden is otherwise prohibited.
  • Would you like to join Diving Club Calypso in a snorkelling trip and monitor the fish with the specialists? Send an e-mail to Calypso. Please note: You must be a well-abled snorkeller or diver! There is a disclaimerpage.

Main goals of our project:

  • Two neighbours spotting a pike

    To get a better insight in the abundance of all species of flora and fauna that inhabit the waters of Leiden (30 mins from Amsterdam).
  • Special interest is in how exactly the animals use the canals (for breeding, feeding etc). And we try and uncover what measures are necessary to keep them (or invite even more of them) here.
  • Another goal is to get the people of Leiden involved in taking care of their environment 'in front of their door'.
  • They can do that by taking out debris with small fishing nets, or by helping with the big cleanup-jobs we organize with our free litterfishing canoos. Join us!
  • But also by spotting, counting and registering the fish they see, 'protecting their pike' (each canal has its own individual, territorial pike) and so forth.

Does this inspire other cities?

  • Aaf's independent bureau of advisory work on aquatic species in the canalsAs projectleader of the succesful fishmonitoring group in the Havenwijk, Ms Aaf Verkade has been asked by the council to extend her activities to new communities in Leiden annually since 2015.
  • If possible, we would like our project to be copied by enthousiastic locals in other cities as well! It worked very well with our 'Feline Lifeline' programme, see below.
  • Aaf enjoys stimulating the locals to clean up the waterways in their communities and care for their 'neigbours under water' - you can hire her to give an inspirational speech (in 5 languages).
  • See her professionalwebsite for more information about her work as an independent City Canal advisor (in Dutch only).

Flashlightfishing, just one of 10 methods we use to count fish

Flashlightfishing, just one of 10 methods we use to count fish

Their first American crayfish! (exotic species, though)

Their first American crayfish! (exotic species, though)

Would you believe this photo was taken in a canal?

Would you believe this photo was taken in a canal?

Our canals are full of (young) fish; at least 22 species!

Our canals are full of (young) fish; at least 22 species!

Handpicked media are invited to interview our team

Handpicked media are invited to interview our team

Missisippi slider turtles, at home in Leiden too

Missisippi slider turtles, at home in Leiden too

A bullhead (rivierdonderpad) saved by Nick

A bullhead (rivierdonderpad) saved by Nick

Trashurehunting in the canals, with unbelievable finds!

Trashurehunting in the canals, with unbelievable finds!

Protected species and amazing discoveries

  • Bullheads help us to design the best hotel as they will be relocated in their native habitatThe most precious species found until now are: eel,  lamprey, spined loach and bullhead.
  • Exotic species, like Chinese mitten crabs and American crayfish have also been discovered, as well as Mississippi slider turtles, which are seen abundantly, caught (snorkelling) and photographed and measured for research.
  • The first exotic goby was discovered in 2015 (the tube-nosed goby) and the second (black goby) in 2018. The latest newcomer is the Caucasian dwarf goby (2022). Their invasion of the Leiden canals is being investigated with a 'goby-grant': Aaf won this special grant from Stichting RAVON.
  • Aaf also discovered a 'flat fish' in the research area Havenwijk-Zuid in 2015, called the flounder, which is a species that uses both salt and sweet water to go through all of its life-cycles.
  • Together with Lilith and Nick she spotted a first live lamprey on 31st May 2021 whist flashlight-monitoring. 

Facebook of big fish

  • Indeed, big fish have (just like dolphins and whales) nicks, scratches and parts of their fins missing, which makes them individually distinguishable.
  • They are catalogued in their own 'Facebook' (Smoelenboek) on this website.

onderwaterinleiden smoelenboek zeelt-
onderwaterinleiden smoelenboek zeelt z-32 becks
z-65 Bami rechterwang
onderwaterinleiden smoelenboek zeelt-
onderwaterinleiden smoelenboek rivierdonderpad
onderwaterinleiden smoelenboek zaklampvissen tekeningen
onderwaterinleiden smoelenboek rivierkreeft
onderwaterinleiden smoelenboek karpers

Cleaning up the clutter under water

  • The bikes and other debris on the bottom are regularly taken out of te water with help of volunteer captains of stichting de Leidse Rederij, locals, volunteers from other cities and the council. Click here for a link.

grijper helping-hand onderwaterinleiden
drijfvuilvissen kanovloot onderwaterinleiden afval
onderwaterinleiden winnaar-fotowedstrijd floorhendriks groot
onderwaterinleiden grofvuilvissen brandweerduiker happy
onderwaterinleiden grofvuilvissen haanstra monique-shaw
onderwaterinleiden grofvuilvissen fiets
onderwaterinleiden grofvuilvissen fietsen
onderwaterinleiden grofvuilvissen bewonersparticipatie
helping-hand-grijper container stortpas zwerfafval

Cleaning up the (floating) debris

  • drijfvuilvissen met de kanovloot van Onder water in Leiden, foto (c) Maryse LorangerWe started a Taskforce with the council, a tourboat company (Stichting de Leidse Rederij), a back-to-work rehab programme and locals with the main goal to regularly clean up the plastic garbage floating in the city. This works a treat!
  • Click here for the Dutch page of Plastic Spotter, who now cleans the canals each sunday.
  • You can also use your own SUP or kayak to have an enjoyable time on the water, whilst helping to clean up our environment, where no one else can reach it.

Project of the KNNV, Leiden dept.

  • Since january 2013, the project 'Monitoring of fish in Havenwijk-Zuid' is one of many projects overseen by the KNNV, Leiden dept.
  • The KNNV dept. of Leiden and surrounding areas, click to visit their websiteThis organization of inspired and enthousiastic (amateur) biologists make sure all data is gathered professionally and processed in such a way, that institutions like the council, Angler's Union Leiden and the watercontrol department (Hoogheemraadschap van Rijnland) can use the data to adjust their strategies and plans regarding water treatment and fishing regulations, if necessary. 
  • They've discovered 26 species of fish, inlcuding the elusive Lamprey and various exotic species.
  • They also published a book about the art of 'flashlight-fishing' (Zaklampvissen: Dutch only), which seems to be the best method to count the abundance of fish in a city environment.

Feline Lifelines

  • Feline Lifelines is a hugely successful programme to ssave your cat from drowning in the canals'.
  • It was started by the locals, with support from the council, in 2009 in the Havenwijk.
  • More information can be found here, since the project has been turned over to another volunteer.
  • Because of its immense success in Leiden (more than 100 cats have been saved from drowning) it has expanded in dozens more cities in the Netherlands.

onderwaterinleiden reddingsnestje meerkoetenfamilie
onderwaterinleiden katuitdegracht kattenklimtouwen meerkoetjes
kug-logo breed
onderwaterinleiden katuitdegracht waterdrinken
onderwaterinleiden aaf kattenklimtouw-inspectie
onderwaterinleiden katuitdegracht reddingsnestje


"Onder water in Leiden" is onderdeel van "Aaf Verkade Adviseur Stadsgrachten"

Voor interviewverzoeken zie de contactpagina

Kijfgracht 12
2312 RZ Leiden

KvK 64674487
BTW nummer NL163735694B01
NL47 Trio 0391068563 t.a.v. Verkade Stadsgrachten

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