Question

Water blooms are formed by
A. Lemna
B. Hydrilla
C. Water hyacinth
D. Planktonic algae

Answer 1

Water blooms include a wide range of marine photosynthetic species, including both macroscopic, multicellular organisms such as seaweed and microscopic, unicellular organisms such as cyanobacteria. The term "water bloom" usually refers to the rapid growth of microscopic, unicellular organisms. Water blooms involve a tremendous increase of microscopic organisms.

Complete explanation:
Option A: On or just under the water's surface, Lemna species emerge as simple free-floating thalli. Except for Lemna trisulca , which is elongated and has a branched structure, the majority are thin, not exceeding 5 mm in length. The single root of Lemna thalli separates it from similar genera Wolffia (no roots), Spirodela , or Landoltia (have multiple roots).
So, option A is incorrect.
Option B: Hydrilla has been naturalized and invasive in the United States as a result of its release from aquariums into Florida waterways in the $1950$s and $1960$s.
So, option B is incorrect.
Option C: Water hyacinth thrives in a variety of freshwater habitats. This plant can grow to be a few inches tall or over three feet tall. The leaves are rounded and leathery, with spectacular lavender blooms linked to spongy and sometimes inflated stems.
So, option C is incorrect.
Option D: Planktonic algae are microscopic plants that float freely on the surface of a body of water. The rapid growth of algae caused by nutrient enrichment in a water body is known as water bloom.
As a result, choice D is the correct answer.

Hence, Option D. is the correct answer.

Note:
An algal bloom, also known as an algae bloom, is a sudden increase or aggregation of algae in freshwater or marine water bodies, and can be identified by the discoloration of the water caused by their pigments. Green algae, blue-green algae, diatoms, and Euglena make up the majority of the planktonic algae population in ponds. Some planktonic algae species, especially blue-green algae, can be toxic to animals and leave an odour or taste in the water.