Description

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Context

Recently bioluminescent blue waves were observed in the backwaters of Kochi attracting tourists but raising concerns among ecologists and fishers due to underlying environmental degradation.

Details

Aspect	Details
Cause	Emission of light by Noctiluca scintillans (dinoflagellate plankton), commonly called Sea Sparkle
Season	Typically observed March to May, locally called Kavaru
Trigger	Mechanical disturbances like waves or movement activate light emitting chemical reactions

Scientific Explanation

Factor	Description
Organism	dinoflagellate
Chemical Reaction	Occurs in structures called scintillons within the organism
Color	Generally blue; can be red or brown depending on bloom density
Ideal Conditions	Salinity: 30–35 ppt Temperature: Warm waters Nutrient Overload: From sewage, industrial runoff
Eutrophication	Excess nitrates & phosphates promote plankton growth causing algal blooms
Red Tides	When concentration exceeds 500,000 cells/litre, visible as red water patches

What Are Backwaters?

Feature	Description
Definition	Backwaters are partially enclosed water bodies formed by the action of tides, where seawater enters the mainland through inlets and estuaries but does not mix completely with freshwater. These are brackish(slightly salty) in nature.
Formation	Formed due to coastal sediment deposition, lagoon development, or river mouths getting blocked by sandbars
Water Type	Mix of freshwater (from rivers) and saltwater (from the sea) — brackish ecosystem
Ecological Importance	Rich biodiversity, support estuarine ecosystems, mangroves, nurseries for marine life
Economic Role	Support fisheries, aquaculture, inland navigation, and tourism (e.g., houseboats in Kerala)

Impacts

Impact Area	Description
Harmful Algal Blooms	Plankton release toxins and chemicals such as ammonium, dimethyl sulphide and organic carbon
Oxygen Depletion	Leads to fish kills and biodiversity collapse
Toxins	Includes domoic acid, paralytic shellfish toxins e.g. from Alexandrium
Fisheries	Loss of fish population → Reduced income for coastal fishing communities
Human Health	Shellfish poisoning → Neurological and gastrointestinal risks
Tourism	Attracts visitors but masks deeper ecological crisis

Backwaters in India

Region	Major Backwaters	Notable Features
Kerala	Vembanad, Ashtamudi, Punnamada, Kayamkulam	Houseboats, tourism, snake boat races; Vembanad is India's longest backwater
Odisha	Chilika Lake (brackish lagoon)	Asia’s largest coastal lagoon, biodiversity hotspot, migratory birds
Tamil Nadu	Pulicat Lake	Second largest brackish water lake in India, bird sanctuary
Andhra Pradesh	Kolleru Lake	Ramsar site, freshwater lake connected to Godavari Krishna delta
Maharashtra & Goa	Mandovi, Zuari	Tidal estuaries with limited backwater system, supports fisheries

Sources:

DOWNTOEARTH

PRACTICE QUESTION

Q. Which of the following best explains the term backwaters as used in the context of Indian geography?

A. A freshwater lake formed by glacial action
B. A section of a river that flows underground
C. A brackish water body formed where seawater enters the land but does not mix fully with river water
D. A region where groundwater meets volcanic activity.

Answer: C

A is Incorrect. This describes glacial lakes not backwaters. Glacial lakes are common in the Himalayas not in coastal India.

B is incorrect. This refers to underground streams or karst topography not backwaters.

C is correct. This correctly describes backwaters, which are coastal water bodies created by the mixing of seawater and freshwater in low-lying coastal areas. The water is brackish and these zones are partially enclosed by land or sandbars.

D is incorrect. This is related to geothermal springs or hydrothermal activity not backwaters.