Create or restore backwater habitats

Overall effectiveness category Evidence not assessed
Number of studies: 1
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

A backwater is a body of water connected to a primary river channel, such as a secondary channel or an embayment. Backwaters typically have slow-flowing or standing water, providing ‘pond-like’ habitat within the river system (Sayer 2014). As such, backwaters can be valuable refuges for anguillid eels and other fish species (Hohausová & Jurajda 2005). The straightening (or ‘channelization’) of rivers has resulted in many backwaters becoming disconnected (Meyer et al. 2013). Backwaters may be created or restored, for example by using the remnants of former river channels (Sayer 2014).

^{Hohausová E. & Jurajda, P. (2005) Restoration of a river backwater and its influence on fish assemblage. Czech Journal of Animal Science, 50, 473–482. https://doi.org/10.17221/4244-CJAS}

^{Meyer A., Combroux I., Schmitt L. & Trémolières M. (2013) Vegetation dynamics in side-channels reconnected to the Rhine River: what are the main factors controlling communities trajectories after restoration? Hydrobiologia, 714, 35–47. https://doi.org/10.1007/s10750-013-1512-y}

^{Sayer, C. D. (2014) Conservation of aquatic landscapes: Ponds, rivers and lakes as integrated systems. WIREs Water, 1, 573–585. https://doi.org/10.1002/wat2.1045}

Study locations

Key messages

One study evaluated the effects of restoring backwater habitats on anguillid eel populations in inland habitats. The study was in the UK.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One controlled, before-and-after study in the UK found that the number of European eels decreased after creating backwater habitats in a section of river, along with removing embankments and restoring meanders, while no change in eel numbers was found in an unrestored site.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A controlled, before-and-after study in 2009–2014 in a stream in Norfolk, UK (Champkin et al. 2018) found that creating backwater habitats, along with removing embankments and restoring meanders, resulted in a decrease in European eel Anguilla anguilla numbers, whilst no change was observed at an unrestored site. Average numbers of European eels were lower after stream restoration work was carried out (27 eels) than before (75 eels). There was no significant difference in average eel numbers at an unrestored site over the same time period (‘before’: 35 eels; ‘after’: 12 eels). In 2009–2010, a 370-m long section of chalk stream was restored by creating six backwater habitats (3–18 m long) from the former channel (August 2010), removing flood embankments (0.4–1-m high; March 2009) and restoring meanders. Small patches of locally-sourced reed sweet-grass Glyceria maxima were planted to stabilize the meanders. A 160-m long section located upstream was left unrestored and used as a comparison. Eels were sampled at the restored and unrestored sites on consecutive days during electrofishing surveys on three occasions before (2009) and four occasions after (2011–2014) restoration.
Study and other actions tested
Referenced paper
Champkin J.D., Copp G.H., Sayer C.D., Clilverd H.M., George L., Vilizzi L., Godard M.J., Clarke J. & Walker A.M. (2018) Responses of fishes and lampreys to the re‐creation of meanders in a small English chalk stream. River Research and Applications, 34, 34-43.

Please cite as:

Cutts V., Berthinussen A., Reynolds S.A., Clarhäll A., Land M., Smith R.K. & Sutherland W.J. (2024) Eel Conservation in Inland Habitats: Global evidence for the effects of actions to conserve anguillid eels. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Eel Conservation in Inland Habitats

Related Actions

Actions	Effectiveness	Studies	Category
Plant bankside vegetation Action Link	Evidence not assessed	1	Synopsis Link
Stabilize riverbanks Action Link	Evidence not assessed	1	Synopsis Link
Raise riverbed levels Action Link	No evidence found (no assessment)	0	Synopsis Link