The main direct impact of mining and prospecting is the addition of silt to the rivers and streams, but the small scale of the operations where the largest tool is a hand spade means that the impact is washed away in the heavy rains and gully washing floods that come every September and October.
The indirect impacts are more significant and the most noticeable is the lack of wildlife in the mining regions. Hunting is permitted on some of the private land and poaching inside the National Park is common. Birds, reptiles (except iguanas which are good eating) and amphibians are easy to spot, but mammals are almost never seen along the sendero de oro, even where it crosses the southern sector of Corcovado.
Other environmental concerns include cutting firewood and the small garbage dumps that accumulate near the camps but these are relatively minor compared to the impact of other rural activities like farming or ranching.
There have never been any big strikes on the Osa, just enough minor successes to keep fortune seekers coming back. Increasing urban unemployment has caused a surge in the numbers along the sendero de oro. It only takes a few dollars worth of equipment to set up camp and get started so we met several mineros who had arrived in the past couple of months after deciding that shoveling gravel was a better use of their time than hoping for a job opportunity in San Jose.