Why was the Panama Canal to difficult to build?

FIRST ANSWER: There were astounding engineering challenges due to the difference in sea level at the Atlantic vs. Pacific sides, but the thing that proved most difficult was the mosquito borne disease. Thousands of French, Panamanian and American workers dies as a result of malaria and other tropical pathogens.

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REPLY BY NigelG: +++

The "Astounding" part of the project was NOT the difference in sea-levels (due to tides). That is no real problem at all, needing only entrance locks as on the earlier, already-successful, Suez Canal. The real engineering difficulties for the Panama Canal were those of building a series of large locks and their feeders to take the canal over the central ridge of the isthmus. ' The first attempt, by the French, failed because the designer, de Lesseps, specified a sea-level route (with tidal locks) but he under-estimated the problems and cost of cutting through the ridge.