Which of the following rivers of Uttar Pradesh has been declared a 'Biological Disaster' due to environmental pollution?

The answer is B) Gomati. The Gomti is the river that was widely reported as a 'biological disaster' because of untreated sewage and industrial effluent. It rises near Madho Tanda in Pilibhit district, flows through Lucknow, Sultanpur and Jaunpur, and joins the Ganga near Saidpur in Ghazipur. Its dissolved oxygen falls very low and its BOD rises sharply in the stretch below Lucknow, which is why it was described as biologically dead.

Why the others are weaker choices:

• Yamuna: Badly polluted, especially in Delhi, but the 'biological disaster' label in this question refers to the Gomti.
• Sai: A small tributary of the Ganga in the Rae Bareli and Pratapgarh belt. It has local pollution but no such national-level label.
• Tamsa: A minor tributary in eastern UP, not the river linked to this declaration.

Core concept: river pollution, sewage and industrial load, and the Ganga Action Plan and Namami Gange programme. For Mains, link this to urban sewage management and the limits of STP capacity in UP towns.

Note that 'biological disaster' is a media and advocacy description, not a statutory category, so check the exact source wording if a question uses it.

Trap: Aspirants pick Yamuna because it is the most famous polluted river. Read the question's wording and match it to the specific report.