The present paper is a part of hydrobiological studies of pools in the Middle -Elbe region, undertaken by the working group of hydrobiologists, headed by DR . J . HRBA6EK .
In this first contribution of a series of littoral studies, the quantity of the littoral zooplankton and the quantity of zooplankton in a part of the backwater, overgrown by submerged vegetation, has been investigated during two summer seasons .
The backwater Labicko is situated on the right bank of the Middle -Elbe, nearly two kilometres north -west from the town of Celakovice, 170 m above sea level . The area is highly productive, agriculturally cultivated land, lying on alluvium . Following the classification of MITIS (1940), the backwater is an "old arm", i .e . an arm in a steady connection with the river . The arm was formed during the regulation of the Elbe River in 1924 . The connecting channel is nearly 100 m long and 1-2 m wide, with a water column, changing in connection with the variation of the flow in the river from 20-60 cm. The bathymetric chart, distribution of macrophytes and situation of the sampling stations is shown in Fig . 1 . The general view of the Labicko is given in Fig. 2. Table I summarizes the mean physical, chemical and biological data of the backwater .
Three stations were investigated regularly ; samples at the fourth station (station A) were taken only from the beginning of 1953 . The vegetation of the stations developed as follows :