Guide 5 of 12

Algae blooms and buying a Pennsylvania lake home

References checked Oct 4, 2026.

Short answer: Pennsylvania publishes harmful algal bloom (HAB) sample results on a public dashboard.¹ Each result is about one sample, at one spot and time, not the whole lake.² State sampling focuses on state-managed waters and private beaches, and the state task force usually has no say over private waterbodies, so many community lakes have few or no samples.²³ Ask who tests the lake you are looking at.

What a harmful algal bloom is

A HAB happens when some kinds of cyanobacteria (often called blue-green algae) grow quickly and can make toxins.⁴ Pennsylvania's Department of Health says HABs most often form in late summer or early fall, and their toxicity can change quickly.⁴ A HAB can't be confirmed by looking at the water; that takes a lab test.³

What the dashboard shows

The Pennsylvania HABs Dashboard combines field and lab data sent in by trained state staff and volunteer groups.² Each point shows the water body's name, the sample date and a response level.² The state task force includes DEP, the Department of Health, DCNR, the Department of Agriculture, the Fish and Boat Commission, the Game Commission and the Pennsylvania Emergency Management Agency.³

The dashboard's user guide lists these response levels:²

• Avoid Contact (Red): the sample's cyanobacteria or toxin levels are potentially harmful.
• Advisory (Yellow): cyanobacteria that could make toxins were found, but not at a potentially harmful toxin level.
• No HAB issue detected: no tested value passed a threshold.
• Waiting on lab results: lab results are expected soon.

The guide says these responses are specific to a sampling event, and that the thresholds are meant for swimming, which has more water contact than other activities.²

DEP's HABs page also describes a Watch recommendation, used to tell the public that conditions could lead to a HAB.³ The dashboard user guide notes that Watch status is not shown on the dashboard.²

How we use the data

We downloaded the dashboard's public data layer. On Oct 4, 2026 it held 3,200 sample rows, with sample dates from 2018 through 2026.⁵ For each lake we profile, we count samples by season (the year of the sample date) and show how many were Advisory (Yellow) or Avoid Contact (Red). We drop rows still waiting on lab results. We never show a "current" status. For recent results, open the Pennsylvania HABs Dashboard itself.¹

Why "no samples" doesn't mean "no blooms"

The dashboard's guide says it is meant to raise awareness of HABs at state-managed waterbodies and private beaches.² DEP says the task force and its agencies do not typically have jurisdiction to regulate HABs on private property or to carry out prevention on private waterbodies.³ So a private community lake can have no state samples at all. On our pages, that shows as: "The PA HAB dashboard data has no samples for this lake (checked [date]). State agencies don't usually sample private lakes, so ask who monitors the water (Question 8)."

Reading a lake's season table

• Look at how many samples there were, not just the colors. Two samples in one summer say little about a lake.
• Look at when. A result from three seasons ago is history, not a forecast.
• Remember the spot. A sample from one cove may not describe the main lake.
• Use the dashboard for anything recent.

The thresholds behind the colors

The dashboard's user guide lists the levels the task force uses. For microcystin, any detection below 8 micrograms per liter (µg/L) is an Advisory (Yellow), and 8 µg/L or more is Avoid Contact (Red); for cylindrospermopsin the dividing line is 15 µg/L.² For cyanobacteria counts, 300 natural units per milliliter is an Advisory and 1,500 is Avoid Contact.² The guide marks the anatoxin-a and saxitoxin values as provisional.²

What the levels mean for people and pets

DEP's page pairs each level with advice. At the Advisory level it says not to swallow the water, to avoid discolored water, algae mats or scum, and to wash with soap and water after contact.³ At the Avoid Primary Contact level it says to avoid activities with a high degree of body contact, such as swimming, water skiing, tubing and children's water play.³ DEP also notes that pets and livestock are often more sensitive to cyanotoxins.³

What a bloom can look like

DEP lists signs that may point to a suspected bloom: water that is usually clear turning bright green or otherwise discolored, water that looks soupy, streaks that look like grass clippings or paint, and scum or mats on the surface or shoreline.³ Only a lab test can confirm one.³

Questions to ask

• Who tests this lake's water, how often, and where are results posted?
• Have swimming areas been closed or posted because of algae? When?
• Does the community have a lake management plan? May I see it?
• What is being done about nutrients reaching the lake, such as from septic systems, lawns or runoff?
• For pets: has the community issued any pet warnings? (DEP notes pets and livestock are often more sensitive to cyanotoxins.)³

FAQ

The lake had Advisory results last summer. Is it safe to swim this year?

We can't say. Results are about single samples.² Check the dashboard for current results and ask who monitors the lake.

Why does my lake have no samples?

State sampling focuses on state-managed waters and private beaches, and agencies don't usually regulate private waterbodies.²³ Ask the community who tests the water.

What is a Watch?

A recommendation the task force uses to say conditions could lead to a HAB.³ It is not shown on the dashboard.²

Can I report a bloom?

Yes. The Department of Health's HAB page links a suspected-HAB reporting form,⁴ and DEP lists the task force email, HABs@pa.gov.³

Lakes where this comes up

• Arrowhead LakeMonroe County
• Gold Key LakePike County
• Harveys LakeLuzerne County
• Conneaut LakeCrawford County
• Deer LakeFayette County
• Indian Mountain LakeMonroe County