Photos of algae have been taken from samples of natural surface waters of South-Transdanubian region; the majority originated from river Dráva and lake Baláta. Images have been made by phase contrast setting, whereas a blue color filter has been used instead of a green one recommended by the literature. The reason of the change is that although the green filter gives a sharp image, it reflects the shades of gray color only. When using a blue color filter, the sharpness of the image is barely reduced, but the colors of the object are retained.