Locals and foreigners may freely cross borders within an 80km radius of Leticia, but a passport is needed for points beyond.
If you plan on heading further afield, you must get your passport stamped at the Ministry of Foreign Relations office at Leticia's airport. Importantly, you must get a second stamp (from either the Brazilian or Peruvian authorities) within 24 hours, so plan carefully. If you have an early departure from Leticia by boat, you'll need to get your stamp at the airport the day before. Citizens of some countries, including the USA, Canada, Australia and New Zealand, need a visa to enter Brazil and it may be costly. To avoid a lot of stress and heartache, it's strongly recommended to arrange your visa before arriving in the Amazon. But if you must, bring a passport photo and yellow-fever vaccination certificate to the Brazilian Consulate. Processing time is one to three days, depending on volume. If you're coming from or going to Iquitos, get your entry or exit stamp at the Policía Internacional Peruviano (PIP) office on Isla Santa Rosa, the Peruvian island facing Leticia. Travelers coming here from Brazil who need a Colombian visa may obtain one at the Colombian consulate in Tabatinga.
If you need a Colombian visa extension, there is no need to pay an extension fee. Simply stamp out and head to Brazil or Peru for one day and return for a fresh 60-day stamp.