Every figure on The Water Almanac comes from a state or federal agency record, and each data block names its agency and the date we fetched it. We do not estimate, round up or fill a gap with prose: when a lake has no record for something, the page leaves it out.
| Agency | What we use | How often we check | Terms |
|---|---|---|---|
| Michigan Department of Natural Resources | Lake outlines, names, acres | When a page is built | Michigan open data, no restrictions on use |
| U.S. Geological Survey, GNIS | Names for lakes the state layer leaves unnamed | When a page is built | U.S. government, public domain |
| Michigan Department of Natural Resources | Measured deepest point | When a page is built | Michigan open data, no restrictions on use |
| Michigan Department of Natural Resources | Depth contours on the lake map | When a page is built | Michigan open data, no restrictions on use |
| Michigan Department of Environment, Great Lakes, and Energy (EGLE) | Water clarity; older depth estimates | When a page is built | Michigan open data, no restrictions on use |
| Michigan Department of Natural Resources, Fisheries Division | Fish stocking records | Daily | Michigan open data, no restrictions on use |
| U.S. Bureau of Land Management, CadNSDI | Survey sections that place each stocking | With each stocking | U.S. government, public domain |
| Michigan DNR Parks & Recreation Division | Public launches and their status | Daily | Michigan open data, no restrictions on use |
| Michigan Department of Health and Human Services | Algae bloom reports and toxin tests | Daily | No licence stated; shown as attributed facts |
| U.S. EPA Cyanobacteria Assessment Network (CyAN) | Satellite cyanobacteria | Daily | U.S. government work; licence not stated on the service |
| Michigan Department of Natural Resources | Trout lake designations | When a page is built | Michigan open data, no restrictions on use |
| Michigan Fish Atlas (MDNR / UMMZ) | Historic fish records | When a page is built | Michigan open data, no restrictions on use |
| National Weather Service | Forecast, weather and fire warnings | Hourly | Public domain (weather.gov) |
| National Interagency Fire Center (WFIGS) | Wildfires and prescribed burns | Hourly | No licence stated; disclaimer only; shown as attributed facts |
| U.S. Census Bureau TIGER | County lines and townships | When a page is built | U.S. government, public domain |
15 sources on Michigan pages. Terms quoted in our source register, checked 6–8 Oct 2026.
A depth marked “measured” is the deepest point Michigan DNR recorded in a lake survey. Some surveys go back to the 1930s; the state still publishes them as its depth of record. By a random sample of 200, Michigan DNR has measured about 34% of the state’s 6,461 named lakes of 10 acres or more.
For many other lakes the only figure is an older estimate from Michigan EGLE. Its depth field is labelled in feet but holds metres, and the values are rounded. Across the 137 lakes in our first four counties that have both, the measured depth is a median 3.4 times the EGLE number; read as feet, the estimate would be less than half the measured depth on 126 of 137. Even converted to feet, it lands within 20% of the measured depth on only 67 of 137. So we convert it, round it to 5 ft, and print it as “about 30 ft (estimate)”. A measured depth always wins.
| Lake | Measured, DNR | EGLE, as published (“ft”) | What we print without a survey |
|---|---|---|---|
| Cass Lake | 123 ft | 36.6 | about 120 ft |
| Lake Cadillac | 25 ft | 7.6 | about 25 ft |
| Meauwataka Lake | 45 ft | 18.3 | about 60 ft |
| Hodenpyl Dam Pond | 70 ft | 21.3 | about 70 ft |
Michigan DNR lake survey deep points; Michigan EGLE inland lake layer. Comparison computed 8 Oct 2026.
Lake maps are drawn from Michigan DNR survey contours. Each band is filled by the depth of the contour that bounds it; the share of a lake deeper than a given depth is measured from those shapes. The maps show a historic survey, so they are not for navigation.
County charts shade every lake by its deepest measured point. Michigan’s township survey lines, which most county borders follow, do not always run true north; Oakland County’s run 1.9° off. We draw each county square to its own survey lines and turn the north arrow so it still points to true north.
Michigan DNR depth contours; U.S. Census TIGER county lines.
Clarity is the depth at which a black-and-white Secchi disk disappears from view. Michigan EGLE estimates it for about 70% of named lakes from satellite images, averaged over 2018 to 2023. It is a long-run average, not today’s water, and clear water is not a test for bacteria or algae toxins.
Michigan EGLE satellite-derived Secchi depth.
Michigan DNR posts each stocking after the fish go in: date, species, number and site. There is no public schedule, so an alert can only follow a stocking, never announce one.
The records name a lake and county but give no coordinates, and many lakes share a name. Oakland County has 4 called Long Lake. Matching by name alone gave all 4 the same 22 stockings. Each record also carries its survey township, range and section, so we place it in the lake inside that section: those stockings belong only to the 166-acre Long Lake in Commerce Township. In Oakland County 775 stockings are placed this way and 0 are left unplaced.
Michigan DNR Fisheries stocking records; U.S. Bureau of Land Management survey sections.
Michigan DHHS keeps two kinds of algae records, and we never mix them. A water sample is tested in a lab for microcystin, a toxin made by cyanobacteria; we compare it with the U.S. EPA swimming guideline of 8 ppb. A bloom report comes from the public and may never be tested; we say “reported, not tested”.
Reports from the last 60 days come first, then the highest toxin level ever measured with its date, then how many samples exist. A recent sample at or above the guideline puts CAUTION on the page.
Michigan DHHS harmful algal bloom records; U.S. EPA 2019 recreational water quality criteria.
EPA’s CyAN satellites estimate cyanobacteria every day on lakes of about 1 km² (247 acres) and larger. Clouds and shorelines hide pixels, so we only read a day when at least 80% of the lake’s usually visible water is visible. This season the 25 satellite lakes in our first four counties had a median of 14 readable days from April to early October. 3 lakes returned identical readings every day; we treat those as not updating and show nothing.
“Satellite detected cyanobacteria across about 30% of the lake” means the satellite saw it on that share of the readable water on that day. It is not a toxin test. Pontiac Lake showed cyanobacteria on 13 days this season; its water sample on 2 September 2026 tested at 22.1 ppb.
U.S. EPA Cyanobacteria Assessment Network (CyAN), daily.
The strip under each lake title is refreshed hourly: the National Weather Service forecast and any warning in effect, including Red Flag Warnings for fire weather; wildfires and prescribed burns within 25 miles by their official type (a prescribed burn is a planned fire, never called a wildfire); the latest readable satellite image; recent bloom reports; and launch status as Michigan DNR lists it. Each line carries the time it was fetched. When a feed does not answer, the line is left out rather than guessed.
For campfires and debris burning we link to Michigan DNR’s daily burn permit page; there is no open data feed for it, and we do not say whether burning is allowed.
National Weather Service; National Interagency Fire Center; U.S. EPA CyAN; Michigan DHHS; Michigan DNR.
We email only when a record changes: a stocking is posted, algae is reported or tested, or the satellite sees a bloom start on two readable days in a row. Lake Mitchell showed cyanobacteria on 36 days in 2026 and would have sent 1 alerts. At most one email a week per lake. A lake with regular stockings or algae records sends one to six a year; a quiet lake may send none, which is why the county alert exists.
Measured from Michigan DNR, Michigan DHHS and EPA CyAN records for 2026.
Some questions people ask about lakes have no reliable public record, and a wrong answer could hurt someone. We do not say whether ice is safe or how thick it is, what the water temperature is, or whether campfires are allowed today. Beach E. coli closures are not covered yet: we have not found an open source for them.
Our source register lists every feed we use; a figure without a source does not ship.
If a figure on a page is wrong, tell us which page and which figure. We check it against the agency record, fix the page, and note the change with its date.
Write to hello@thewateralmanac.com.
Corrections are logged with the date of the fix.