What type of algae is described as microscopic plants usually suspended in the upper few feet of water and can reach bloom proportions?

Planktonic algae are indeed described as microscopic plants that typically float in the upper layers of water, where they can receive adequate sunlight for photosynthesis. This type of algae is critical to aquatic ecosystems as it serves as a primary food source for many aquatic organisms. When conditions are favorable, such as high nutrient availability and warm temperatures, planktonic algae can proliferate rapidly, resulting in what is known as algal blooms. These blooms can significantly affect water quality and aquatic life, as they may block sunlight from reaching submerged plants and can lead to oxygen depletion in the water when they decompose.

In contrast, filamentous algae are characterized by their long, thread-like structures and often form mats on the surface of water bodies but do not exist in microscopic form suspended in the water column. Eurasian watermilfoil and curly-leaf pondweed are actually aquatic plants, not algae, and while they can also contribute to water quality issues, they do not bloom in the same way that planktonic algae do.