Water pollution represents a major environmental problem, which has been around for decades, maybe even longer, and is getting more and more serious, determining the need for effective, precise and if possible cheap methods of monitoring and evaluating its impact on aquatic ecosystems. Algae, as photosynthetic organisms, have gained considerable attention as reliable biological indicators of water pollution due to their high sensitivity to environmental changes and their wide distribution in all categories of aquatic habitats. The unique characteristics of algae, a wide variety of species, and their ubiquity in different types of water make them suitable candidates for such indicators. Algae respond rapidly to changes in water chemistry, temperature and nutrient levels, making them sensitive to various types of pollution, including heavy metal pollution, organic pollutants and excess nutrients different methods and techniques can be used to measure and evaluate the responses of algae to water pollution, determining both quantitatively and qualitatively the level of pollution. These techniques range from traditional microscopy-based identification and enumeration to more advanced molecular methods such as DNA barcoding and high-throughput sequencing. In addition, the use of bioindicators derived from algal communities, such as algal and biotic indexes, is discussed as a valuable tool in water quality assessment. The potential of algae to detect and monitor pollution events, assess the ecological health of water bodies, and evaluate the effectiveness of pollution control measures is high and incompletely exploited in Romania and beyond. Factors such as natural variability, species-specific responses, and the need for standardized protocols, emphasizing the importance of considering these factors when interpreting algal data are crucial issues and still need to be well established. The continuation of research in this field is crucial for perfecting the use of algae as indicators and the development of internationally standardized protocols (EU and not only) for their application in water quality assessment.