Category Rivers

What is harmful algal bloom?

Recently, Lake Merrit in Oakland, California, the U.S… turned reddish brown, causing fear among the residents. They were advised to not use the water and to keep their pets away from the water body. Scientists suspected a possible case of Harmful Algal Bloom (HAB), and the samples have been sent for investigation. This is not the first time that HAB has been experienced in the lakes in the US. In the last few months, there has been a sporadic rise in the detection of algal bloom in the lakes. Lakes such as Hopatcong, Anna, Erie, and so on have been witnessing the highest concentration of HAB, triggering concerns.

Algal bloom is an overgrowth of algae or algae-like bacteria in fresh, salt, or brackish waters. They can occur in a variety of colours, namely red, blue-green, brown, and pink. Depending on the algae, they can lead to the formation of scum, foam, froth, or a slick. Not all algal blooms are toxic. A HAB, though, is, and can endanger humans and many organisms.

What causes HAB?

Most are caused by cyanobacteria. Though they are bacteria, they perform photosynthesis just like algae, and are often called blue-green algae. Some produce dangerous cyanotoxins. The most reported cyanobacteria is microcystis. HAB Occurs naturally as well as due to human activities. In fact, human activities such as the burning of fossil fuels, land development, and deforestation have all led to an increase in the amount of carbon dioxide. The cyanobacteria feed on the carbon dioxide, which fuels their growth.

Most harmful algal blooms are caused by cyanobacteria. Though they are bacteria, they perform photosynthesis just like algae, and are often called blue-green algae.

Picture Credit : Google 


The pelagic zone is the open region of any lake, sea, or ocean that is away from any part of land, be it the coast or the sea floor. Marine life-from microscopic plankton and tuna to sharks – dominates this area. Due to the abundance of marine creatures, it is a critical space for producing oxygen, regulating climate, and economic activity.

Pelagic Zone Facts

The pelagic zone plays many critical roles that make it essential to life on Earth. Factors that make the pelagic zone unique include:

It covers more than 50% of the Earth in water, more than 3.2 kilometers (2 miles) deep.
It makes up more than 99% of the inhabitable space on our planet.
The deepest part of the ocean, the Mariana Trench, is about 11,000 meters (7 miles) deep.
The open ocean produces more than 50% of the world’s oxygen.
It is a critical carbon sink, storing 50 times more carbon dioxide than the atmosphere.
Many of its inhabitants never experience sunlight.

The open ocean provides food, medicine, and economic opportunities for people worldwide. In addition to seafood, ocean harvests provide ingredients for foods like peanut butter and soy milk. Medications for Alzheimer’s disease, cancer, heart disease, and arthritis use materials extracted from the ocean, and the United States alone produces $282 billion in ocean-dependent goods and services.

Layers of the Pelagic Zone

The pelagic realm is divided into five distinct regions based on average depth and sunlight availability. Moving from the surface to the ocean floor, the zones are labeled:


Sunlight, oxygen, and temperature decrease with depth while pressure increases. The organisms in each zone have adapted to live in these conditions.

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Pucture Credit : Google