It's possible to visit the Pantanal year-round, but it's best to go during the dry season (May to September). The best time to watch birds is from July to September, when the waters have receded and the bright-green grasses pop up from the muck. If you are on the trail of the elusive jaguar, then you will need to visit June to August, when it is access-all-areas and you can probe deeper into the wilderness.
Flooding, incessant rains and heat make travel difficult during the wet season (November to April), though this time is not without its special rewards – this is when the cattle and wildlife of the Pantanal clump together on the cordilheiras. However, the islands are covered with dense vegetation that can make spotting wildlife difficult. The heaviest rains fall in February and March. Roads become impassable and travel is a logistical nightmare.
From June to August, the driest months, the chances of spotting jaguars rise dramatically. The heat peaks from December to February, when temperatures higher than 40°C (104°F) are common, roads turn to breakfast cereal, and the mosquitoes are out in force. Many hotels close at this time and in the northern Pantanal tour companies effectively take a break.
Fishing is best during the first part of the dry season (April to May), when the flooded rivers settle back into their channels, but locals have been known to lasso 80kg fish throughout the dry season. This is some of the best fishing in the world. There are three species of piranha, as well as the tasty dourado (known locally as the river tiger) that reaches upwards of 9kg. Other excellent catches include pacú, suribim, bagre, piraputanga, piapara, cachara, pirancajuva and pintado, to name but a few.
Although hunting is not allowed, fishing – with the required permits – is encouraged between February and October. It is, however, prohibited during the piracema (breeding season) running any time between November and March. Banco do Brasil branches issue permits valid for three months for fishing in the Pantanal, but you'll need to print off the application form at www.imasul.ms.gov.br first. National fishing permits valid for one year are also available from IBAMA offices in Campo Grande, Corumbá and Cuiabá.