Which of the following best describes the growth conditions for filamentous algae?

Filamentous algae are commonly found in environments that exhibit stagnant, high-nutrient conditions. In these settings, there is less water movement, which allows for the accumulation of nutrients, particularly phosphorus and nitrogen, that promote algal growth. Stagnation can lead to eutrophication, where nutrient-rich waters contribute significantly to the proliferation of filamentous algae.

High nutrient levels are often a result of agricultural runoff, wastewater discharge, or poor water management, which create ideal habitats for filamentous algae to thrive. The absence of rapid water movement in stagnant waters means that these algae can attach and grow freely, leading to dense mats that can affect aquatic ecosystems by blocking sunlight and disrupting the natural balance of the habitat.

In contrast, filamentous algae do not typically thrive in rapidly flowing waters, saline conditions, or deep cold waters as these environments either do not support the growth of filamentous forms due to lower nutrient availability or unsuitable physical conditions.