(#1 Trap):
Students confuse between 'longest river IN India' vs 'longest river OF India'. Ganga is longest river OF India (entirely within India - 2,525 km), but Indus is longer IN India if you count total length (3,180 km total, but most flows through Pakistan). Always read the question carefully - 'in' vs 'of' makes the difference.
Lake Classification System:
Freshwater: Dal, Nagin, Wular, Nainital, Bhimtal
Saltwater: Sambhar, Pachpadra, Didwana
Lagoons: Chilika, Pulicat, Vembanad
River Joining Points (Sangam):
Prayagraj - Ganga + Yamuna + Saraswati (Triveni Sangam)
Devprayag - Alaknanda + Bhagirathi = Ganga
Rudraprayag - Alaknanda + Mandakini
Dam Connection Strategy:
Major rivers have major dams - Ganga (Tehri), Narmada (Sardar Sarovar), Krishna (Nagarjuna Sagar).