Locustella fluviatilis is a widespread summer visitor to central and eastern Europe, which constitutes >75% of its global breeding range. Its European breeding population is very large (>1,900,000 pairs), and was stable between 1970-1990. The species remained stable overall during 1990-2000, with the stronghold population in Russia probably stable, and stable or increasing trends across much of the rest of Europe.

Breeds in upper middle and middle latitude s of warm continental boreal, temperate, and stepes zones of west-central Palearcic. Requires ample stands of very dense but rarely tall vegetation, growing on shady bare soils, accessible to foraging and easy, concealed movement. Such cover may include thickets of grass and nettles among young growth of hazel, dogwoom, alder, birch, hornbeam, willow, and other trees characteristic of moist carr woodland and of floodlands, backwaters, damp fores clearings, bottmlands, bogs, sedge marshes, and even parks sometimes within cities.

Breeds May-July in Eastern Europe. Nest site is built on or within 30 cm of ground in thick vegetation or at base of bush. Nest, loose cup of grass stems and leaves, lined with finer grass and hair. 5-6 eggs are laid, incubation 11-12 days, by female only.

Flying and non-flying arthropods, especially Bugs, True Flies, small beetles, and spiders. Food obtained in dense herbaceous and bushy vegetation, by running about in grassy vegetation, and among fallen leaves of alder and nettles on in woods along rivers and streams. Prey tamen directly from plants and ground, rarely in the air.

This species has a large range, with an estimated global Extent of Occurrence of 1,000,000-10,000,000 km². It has a large global population, including an estimated 3,800,000-9,200,000 individuals in Europe (BirdLife International in prep.). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.

Migratory. Winter quarters not well known, but lie from northern South Africa north to Zambia, Mozambique, and perhaps extreme south of Malawi. Migration very inconspicuous, perhaps due (in autumn) as much to skulking behaviour as to long-distance flights, as span of dates suggests passage protracted; no staging posts known within Europe. General direction is via east Mediterranean and Levant, requiring south-east heading for western breeders, and progressively more westerly heading for eastern breeders.