Final answer:
A nutrient-poor lake with low primary productivity is known as an oligotrophic lake, which has limited phytoplankton growth due to low levels of nutrients like nitrogen and phosphorus. Excess nutrients can cause cultural eutrophication and dead zones where oxygen depletion kills most marine life.
Step-by-step explanation:
A nutrient-poor lake with low primary productivity is referred to as an oligotrophic lake. In these environments, the lack of nutrients such as nitrogen and phosphorus limits the growth of phytoplankton, the foundation of the aquatic food web. Contrastingly, when these nutrients are abundant, often due to human activities like runoff from fertilized lawns and sewage, it can lead to excessive algae growth. This condition, known as cultural eutrophication, can create dead zones where oxygen is so depleted that most life cannot survive. The area becomes hypoxic due to the decomposition of algal blooms, destroying aquatic habitats and making it difficult for organisms to thrive.