holtágak

Holtágak are abandoned or inactive branches of a river channel found in floodplains. The term, used in Hungarian hydrology, refers to river arms that no longer form a part of the active river network. A holtág can appear as a U-shaped oxbow lake when the connecting neck is cut off, or as a disused arm that remains intermittently or seasonally wet.

They form mainly through river meandering and cutoff processes. When a river cuts through the neck of a meander during high flow, the main channel bypasses the bend, leaving behind a separated watercourse. Over time, sediment fills the former channel and vegetation colonizes, eventually producing a wetland or dry meadow depending on drainage. In some cases, avulsion creates a new channel and leaves behind a holtág.

Holtágak are typically located in broad floodplains and lowland river systems. They often contain fine alluvial sediments, have slow or stagnant water, and can exhibit marshy margins and thick aquatic vegetation. Water levels can be seasonal, with more regular inundation during floods.

They serve as habitats for wetland plants, amphibians, birds, and fish; they also act as floodplain reservoirs, slow down runoff, and contribute to groundwater recharge and sediment trapping.

Historically and in contemporary land use, holtágak may be managed for biodiversity conservation, flood mitigation, or as parts of agricultural drainage systems. Their preservation or restoration is a common objective in river restoration projects.