The availability and quality of water determines the living conditions on Earth. Water is irreplaceable component of the nature and environment from biological and social point of view. Surface waters are often negatively affected by anthropogenic activity, which causes the contaminants, to get into the surface waters. Presented bachelor thesis contains literary research about surface waters, provides an overview about indicators of water properties and also about experience with usage of the test organisms for toxicity assessment in waters. Based on the available information is prepared an overview of the monitored qualitative indicators of a small water source - river Krupinica. By evaluating the available results in five monitored sampling points on the section of this river revealed the impact of anthropogenic activity in sections with increased population density, with intensive agriculture and also industrial activities in these areas. It follows that even smaller surface water sources need to be paid attention.