From each sampling area within a pond, bottom sediment containing snails was filtered with a sieve.
Processing of snail samples from 1 pond began in a laboratory about 1 h after sampling and was completed before continuing with the next pond. Snails were individually transferred to approximately 3 ml cercariae-free
drinking water in glass tubes at approximately 24 ◦C. After 24 h, shell height, and the number of cercariae shed was counted on a grit by stereomicroscope (for 65% of snails duplo counts were made by one person, and the two counts were averaged), and cercariae species were identified according to standard keys (Ditrich et al., 1992; Schell, 1985; Scholz et al., 2000; Whitfield et al., 1975).
Snails that did not shed cercariae were crushed and observed under stereomicroscope. If rediae or cercariae were present, this snail was recorded as false-negative.