Book excerpt: The text covers the problems concerning optical properties and remote sensing of turbid and surface-polluted oceans and lakes. In four chapters Helgi Arst compares remote sensing data with data collected from similar examination of clean waters. Chapter 1 provides an overview of the main radiative and remote sensing characteristics and provides discussion on the properties of optically active substances (OAS) in the water and their variability and concentration, drawing on original data obtained in the Baltic Sea region. Chapter 2 focuses on the investigation of the influence of surface oil slicks on the reflection and absorption of solar radiation for both calm and ruffled sea surfaces. A model is provided for determining the temperature and the reflected component in upwelling rough seas. Chapter 3 provides remote sensing results obtained mainly for the Baltic Sea region, including some lakes. Correlations between the concentrations of OAS, water transparency and total remote sensing reflectance are investigated. Chapter 4 deals with subsurface irradiance and optical classification of turbid waters. This chapter analyses the different criteria of the euphotic depth, drawing on a semi-empirical model for the estimation of underwater light scattering. The conclusion provides discussion on the results obtained.