Eel bucks are a type of fish trap

Fish trap

A fish trap is a trap used for fishing. Fish traps may have the form of a fishing weir or a lobster trap. A typical trap might consist of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of...

 that was prevalent in the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 in England up to the 20th century. It was used particularly to catch eel

European eel

The European eel, Anguilla anguilla, is a species of eel, a snake-like, catadromous fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m....

s which were a staple part of the London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 diet.

Eel bucks were baskets made of willow

Willow

Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

 wood, and were often strung together in a fishing weir

Fishing weir

A fishing weir, or fish weir, is an obstruction placed in tidal waters or wholly or partially across a river, which is designed to hinder the passage of fish. Traditionally they were built from wood or stones. They can be used to trap fish...

. Construction of such weirs was outlawed under the terms of Magna Carta

Magna Carta

Magna Carta is an English charter, originally issued in the year 1215 and reissued later in the 13th century in modified versions, which included the most direct challenges to the monarch's authority to date. The charter first passed into law in 1225...

All fish-weirs shall be removed from the Thames, the Medway, and throughout the whole of England, except on the sea coast.

However the practice continued unabated, often with adverse effects on navigation.

Several islands in the River Thames reflect the presence of bucks at those points - for example Buck Ait

Buck Ait

Buck Ait is an island in the River Thames in Oxfordshire, England. It is on the reach above Shiplake Lock near Sonning.The island is uninhabited and tree covered but sits opposite houses with extensive river frontages...

 and Handbuck Eyot

Handbuck Eyot

Handbuck Eyot or Handbuck Ait is an island in the River Thames in England near the villages of Shiplake, Oxfordshire and Wargrave, Berkshire. It is on the reach above Marsh Lock....

.