The bow of the Danube along Érd’s eastern border forms a belt of low-lying, silt-covered land 9 km long and 2-3 km wide, stretching from Háros Island in Budafok down to the Ófalu (Old Village) district of Érd. At the end of the Miocene, this formed part of a shallow bay of the Pannonian Lake. Sand, gravel and clay deposits from this period have survived on the surface around Diósd. The reasons behind the formation of the Érd-Tétény Bend are tectonic. By the end of the Pleistocene, the area had sunk to such an extent that the branches of the Danube moved here from further east.
 
Previous levels of the river can be seen in the remains of the gravel terrace on the edge of the Tétény Plateau between Érdliget and Budafok. These were identified by the great geographer Béla Bulla. The gravely Danube sediment of the Quaternary era form a layer 10-15 m deep, over which there is a 5-8 m depth of sand, flood-plain silt and occasional soil-like loess. This belt of land is only a few meters above the mean level of the Danube and still counts as a flood plain. There is a stone tablet in Ófalu recalling the floods of 1838, 1876 and 1941, when the river burst its banks and inundated the whole area.
 
The danger of flooding explains why the area has remained almost untouched. Various marsh-loving orchids can be found, including the May to June-flowering Orchis palustris and much rarer lady orchid (O. purpurea), a flower with a tropical look, of which a few examples have been found on the loess slope above Ófalu. Unfortunately plants such as these have become much rarer owing to grazing, water pollution and use of chemicals, and many rarities have fallen victim to a new relief road parallel to the river. A typical plant of this belt of land is a relative of the pasque flower, Pulsatilla halleri ssp. Grandis, with lavender, silky-haired flowers opening in the spring.
 
The inhabited parts of the area are protected by dykes, but Beliczay Island has survived almost undisturbed, as the part of Érd where the landscape has most faithfully preserved the original appearance. (It was a strong inspiration to the outstanding Érd artist Gyula Szepes (1902-1992), who captured the enchantment of the Danube banks and Beliczay Island in several paintings.) The area is still inundated from time to time. Before the Danube dykes were built, there was a typical wetland vegetation of reeds and rushes in the lower-lying parts and round the backeaters remaining from the floods, with the sedge Carex elata as the dominant plant.
 
The areas of marsh behind the dykes were drained, so that the wetland vegetation died out or became confined to the banks of the Sulák Brook. The annual flooding of the Danube used to cover the riverside flats with fertile silt rich in humus, which the smaller Benta Brook can no longer do, due to human intervention, regulation work and diversion into a concrete bed. As a result, the abundant water of spring and early summer is followed by a summer water shortage.
 
Typical of these parts is the silvery fringe woodland by the Danube, its most characteristic trees being white willow (Salix alba), crack willow (S. fragilis) and black poplar (Populus nigra), with sporadic purple osier (S. purupurea), almond-leafed willow (S. triandra) and white poplar (P. alba). A picturesque sight are the vast specimens of grey poplar (P. canescens). The atmosphere of a primeval forest is lent by the dewberry (Rubeus caesius), wild vine (Vitis sylvestris) and light-seeking traveller’s joy (Clematis vitalba) climbing through the trees and shrubs.
 
The plant community of the water meadows and reed beds has shrunk considerably due to continual drainage, in-filling and tipping of rubbish. On the remaining areas subject to flooding, defined beds of reeds (Phragmites communis) and accompanying patches of bulrush (Typha latifolia) can still be found. Beliczay Island is an angler’s paradise, with barbell and starlet common in the Danube and bream, pike and wall-eye pike also caught. A few decades ago, wells were not uncommon either. The amphibians found on the island are tree frog, common toad and edible frog. Older inhabitants of Érd also remember the now rarely found grass snake.