Abstract: The sampler is intended to hold a plurality of microscope slides which, in use, are disposed just below the water surface. In use, the sampler holds the slides in parallel spaced relation to each other by means of a slide holder which has a pair of oppositely disposed channel-shaped side members that pivot between a slide-holding position whereat the ends of each slide project into the channel and a slide-releasing position whereat each slide can be easily grasped by its edge and removed. The slide holder is held by a wire bail and a retainer clip so that the side members cannot pivot from their slide-holding position thereby preventing the slides from falling from the holder. The bail itself is pivoted to two floatation members and shaped to dispose the slide holder at a location displaced away from the pivot axis through each floatation member thereby making the sampler capsize-proof because the slide holder will pivot to a position below the water surface even if the sampler is turned over.