PERMANENT_ID		ID number for each lake that corresponds to high-resolution USGS National Hydrography Dataset
lake.name		name of each lake (standardized across all files)
date			date of measurement in YYYY-MM-DD format
year			year of measurement, four digit format
month			month of measurement, values range 5-9
day				day of measurement, values range 1-31
secchi			Secchi disk measurement in meters for each sampling event, resolved to 0.1 m 