Summer in the lowlands can be utterly miserable, with mud, high humidity, biting insects and relentless tropical downpours. However washed-out roads necessitate an increase in river transport, making summer the best time to hop on a cargo boat. Winter in the Altiplano means extreme heat during the day, and freezing winds and subzero temperatures at night. The highland valleys are refuges, having a comfortable climate with little rain year-round.
August is the most popular month of the high tourist season which runs from late June to early September: it has the most reliable weather, is the time of European and North American summer holidays and of most of Bolivia's major festivals, so many Bolivians and South Americans also travel at this time. This can be an advantage if you are looking for people to form a travel group, but prices are generally higher than during the rest of the year.
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