Climate change and anthropogenic activities have intensified freshwater algal blooms, creating substantial risks to aquatic ecosystems and human health. Although traditional in-situ monitoring methods deliver accurate measurements, their spatial and temporal limitations have driven a shift towards remote sensing as a viable alternative with extensive monitoring potential. This chapter reviews recent advancements in spectral indices for detecting and monitoring freshwater algal blooms, tracing their evolution from primary vegetation indices to specialised algorithms. Key indices, including the Normalized Difference Chlorophyll Index (NDCI), Floating Algae Index (FAI), and Algal Bloom Detection Index (ABDI), along with new approaches for macroalgal detection, are analysed for their strengths and limitations across different remote sensing platforms. While these indices enhance the capability to track algal blooms across diverse spatial and temporal scales, challenges remain regarding universal applicability and species-level discrimination. The chapter identifies research gaps and proposes future directions, emphasising the need for integrated monitoring frameworks and standardised methods across satellite platforms to improve algal bloom detection and risk management.