Pollution of water resources is one of the main causes of environmental pollution along with air pollution.

The quality and availability of water resources are undoubtedly one of the great challenges of our century. Its preservation requires better management of pollutants, mainly resulting from human activities.

The pollution of water resources is characterized by the presence of microorganisms, chemicals, or industrial waste. It can concern rivers, water tables, saltwater, but also rainwater, dew, snow, and polar ice. This pollution can have various origins:

Industrial pollution: with the discharges of chemicals such as hydrocarbons or PCBs discharged by industries as well as water discharged by factories

Agricultural pollution: with animal waste but also plant protection products/pesticides (herbicides, insecticides, fungicides) contained in fertilizers and used in agriculture. They then penetrate the soil until they reach the groundwater.

Domestic pollution: with wastewater from toilets, cleaning or cosmetic products (laundry soaps, detergents), paints, solvents, waste oils, hydrocarbons, etc.

Accidental pollution: the accidental spillage of toxic products into the natural environment and which disrupt the ecosystem.

The different types of pollution are:

Organic pollution

It concerns pathogenic microorganisms present in water such as bacteria and viruses. This bacteriological pollution is characterized by a high rate of fecal coliforms.

Organic pollution comes mainly from excrement, household waste, and plant waste

Chemical pollution

It concerns nitrates and phosphates contained in pesticides, human and veterinary medicines, household products, paint, heavy metals (mercury, cadmium, lead, arsenic, etc.), acids, as well as hydrocarbons used in industry.

Focus on drug-derived micropollutants

Advances in medicine are continuously improving human (and animal) health and saving lives. On the other side of the coin, residues of medicinal substances are sometimes found in very low doses in the natural environment (rivers or rivers) or in wastewater from chemical and pharmaceutical industries, with the consequence of an imbalance of the aquatic ecosystem (flora and wildlife).

Regards

Hi I'm from Bangladesh. Here aquatic environment (surface water) is contaminated by different toxic heavy metals (e.g., Fe, Mn, Cd, Cu, Zn, Pb etc.), and pesticide residues. Moreover groundwater is contaminated via arsenic, iron, manganese along with other metals. Salinity intrusion from in coastal area is also contaminated the freshwater resources in this area.

Pollution on freshwater ecosystems is one of the major threats to the biota worldwide. Population growth and human activities are immensely contributing to the degradation and pollution of the freshwater. Freshwater sources, both surface and groundwater are contaminated with different kinds of pollutants (toxic metals and pesticides) discharged from different sources. Various human activities are the main reasons contributing to the decline in quality of freshwaters. The toxic pollutants have adverse effects on aquatic ecosystems and are responsible exclusively or in combination for causing lethal diseases to humans.

Hope, this paper may be of help.

Best wishes !

They are : habitat modification, fragmentation, and destruction; invasive species; overfishing; environmental pollution; forestry practise; and climate change.

Full details in the link:

https://www.iucnffsg.org/freshwater-fishes/major-threats/

quality of fresh water from river, lake, tank and others are very much depends on anthropological pollution. Bacteriological pollution can not be ruled out.