What is the highest lake area coverage of a country?
Lake area coverage = [sum(area of the lakes in the country) / (area of the country)] * 100%
SELECT T2.Area * 100  / T3.Area FROM located AS T1 INNER JOIN lake AS T2 ON T1.Lake = T2.Name INNER JOIN country AS T3 ON T3.Code = T1.Country ORDER BY T2.Longitude DESC LIMIT 1