I'm reading Michel Danino's The Lost River, On the trail of Sarasvati. He mentions the following two verses (#5 and #6) in the Nadistuti Sukta of Rg Veda. (Griffith 10.75.5-6)
O Ganga, Yamuna, Sarasvati, Shutudri (Sutlej), Parushni
(Ravi), hear my praise! Hear my call, O Asikni (Chenab)
Marudvridha (Maruvardhvan), Vitasta (Jhelum) with
Arjikya and Sushoma.
First you flow united with Trishtama, with Susartu and
Rasa, and with Svetya, O Sindhu (Indus) with Kubha
(Kabul) to Gomati (Gumal or Gomal), with Mehatnu to
Krumu (Kurram), with whom you proceed together.
Thats 19 rivers! Two more rivers Silamavati and Urnavati are mentioned in verse 9.
As Michel Danino's explains thats a birds-eye view sweeping (east to west) across more than a thousand kilometers! This sukta seems to be an amazing source of information on Vedic geography.
more on the wikipedia page.