How we gather, date and fade the facts

What we publish. Only public, lake-level facts and general Pennsylvania due-diligence know-how. We don't evaluate homes, communities or dams, and we don't publish rankings.

How we choose lakes

A lake gets a profile when three things are true: it is an inland Pennsylvania lake (not Lake Erie and not a river); a cited source shows homes on or next to its shore, or the lake sits at the center of a residential community; and we could check at least four facts about it. For the second test we use encyclopedia descriptions and U.S. Census Bureau places. The Census Bureau describes census designated places as settled concentrations of population that must include some residential population or housing.¹ When a lake lies inside a Census place named for it, we treat that as a residential community centered on the lake and cite the place's 2020 housing-unit count.² We keep the evidence for every lake, including the ones we left out.

Dams (D1). From the U.S. Army Corps of Engineers' National Inventory of Dams public data service.³ We match dams to lakes by distance from the dam point to the lake outline and by name, and we record that evidence. We show hazard potential with a fixed explainer, condition with its date or 'not reported', year completed, owner type, regulator, EAP status as reported, last inspection reported and the NID record date. We never store or show the names of dam or property owners.

Algae (D2). From the PA HABs Dashboard's public data layer.⁴ A sample belongs to a lake when its point lies inside the lake outline or within 150 meters of it (unless the sample names a different water body), or when its water-body name is a known variant of the lake's name and the point lies within 1 kilometer. We drop rows still waiting on lab results. The season is the year of the sample date. Samples we can't match are listed in our dataset files, not dropped silently.

Public launches (D3). From the PFBC Access Areas layer published through DEP's eMapPA map service.⁵ A launch counts as on the lake when a public access with a ramp lies within 150 meters of the outline. Otherwise we name the nearest listed public ramp and its straight-line distance. We never name private marinas or their owners.

Outlines and municipalities (D4). Lake outlines come from the USGS National Hydrography Dataset.⁶ Shoreline municipalities are the townships and boroughs whose boundaries, from DEP's eMapPA municipal layer, touch the lake outline buffered by 25 meters.⁷

Who owns or controls the lake (D5) and motor rules (D6). One cited sentence per lake where a source supports it. Motor rules appear only for public waters, from PFBC or Pennsylvania's boating regulations.⁸ On private lakes we say: 'Set by the lake's owner; ask (Question 6).'

Municipal links (D7). We link the municipality's website, its zoning page and any short-term-rental ordinance page we find online, each with the date we checked it. If we don't find a rental ordinance, we say so with a fixed sentence. We never summarise ordinance terms.

Laws (D8, D9). We quote or summarise the statute or regulation and link the source, with the date we checked it.

Dates and fading. Every fact shows the date we checked it. After 12 months it turns amber: 'Checked {date}, over a year ago. Check the source.' After 24 months it is greyed out and marked 'Out of date:', it leaves our structured data and share images, and dossier sales for that lake pause. Separately, when a source's own record is more than three years old, we say so: 'This is an older record: {source} last updated it on {date}.'

Reader flags. Anyone can flag a fact as out of date. When three different readers flag the same fact within 30 days, we add: 'Readers report this may be out of date. Check the source.' Flags never change a value. They fade after 30 days.

No live data. We don't show live algae status, water levels, closures or anything else that changes day to day. For current algae results, use the PA HABs Dashboard.

The name. There is no lake named Lake Pennsylvania. This site is about Pennsylvania's inland lakes, not Lake Erie.

Yearly refresh. We can re-run the whole data build in about half an hour. Until we do, the dates tell you how old each fact is.

All sources with datesDownload the datasetCorrections