What characterizes an oligotrophic lake?

An oligotrophic lake is characterized by its clear waters and low nutrient levels, resulting in low productivity. However, it is typically high in dissolved oxygen, especially in deeper areas. This quality is due to the lake's depth, which allows for oxygen to be replenished and prevents stratification that might limit oxygen availability. The limited nutrients lead to minimal algal growth, contributing to the lake's clarity. Conditions like these support certain types of fish and aquatic life that thrive in well-oxygenated environments, making oligotrophic lakes vital for biodiversity.

The other options describe characteristics of lakes in different trophic states. The mention of high nutrients, low dissolved oxygen, pollution, or algae prevalence does not align with the defining features of an oligotrophic lake. Thus, the correct answer reflects the fundamental aspects of oligotrophic lakes regarding their nutrient status and oxygen levels.