The Charles is one of the first places many students discover when they arrive in Boston.
It becomes part of the route to class, the morning run, the weekend walk and the first few weeks of exploring the city.
Right now, part of that experience comes with an active public-health advisory.
The Boston Public Health Commission expanded its cyanobacteria advisory on August 27 after Massachusetts health officials found cyanobacteria above the state guideline for recreational water.
The advisory now covers the Charles River Lower Basin at all points downstream of Boston University’s Duan Family Center for Computing & Data Sciences, also known around campus as the Jenga Tower.
As of September 1, the advisory remains in effect.
What is actually happening in the water?
Cyanobacteria occur naturally in freshwater and can multiply rapidly under certain conditions, creating harmful blooms.
Some blooms can produce toxins that affect people and animals. The water may sometimes look green, cloudy or paint-like, but appearance alone cannot tell you whether a bloom is toxic.
In this section of the Charles, officials found cyanobacteria levels above Massachusetts guidelines for recreational water.
That does not mean Bzzpost is saying toxins were confirmed in this specific bloom.
It does mean health officials are advising people to avoid direct contact with the affected water and impacted shoreline, including swimming and other water activities.
People should also stay away from visible concentrations of algae.
Walking or running along the river is different
The advisory does not mean you need to stop using riverfront paths for a walk or run.
The main concern is contact with the affected water and algae along the shoreline.
So if the Charles is part of your running route, you can still use the surrounding paths while staying out of the water and away from areas where algae has collected near the edge.
That distinction matters.
A health advisory on the river does not automatically mean the entire riverfront is closed.
If you have a dog, pay extra attention
The warning matters especially for pet owners.
Health officials say dogs should not swim in or drink from the affected water, and pets should be kept away from algae concentrations and the impacted shoreline.
If you or your pet comes into contact with the affected water or algae, BPHC advises rinsing off immediately.
Dogs can ingest water much more easily than someone walking along the river, so keeping them away from the edge is the safer move while the advisory remains active.
How long will this last?
There is no fixed end date.
Massachusetts health officials will continue monitoring the bloom and begin follow-up laboratory sampling once conditions improve.
Before the advisory can be lifted, the state requires two rounds of samples collected one week apart to show cyanobacteria levels below the applicable recreational-water threshold.
For this advisory, that threshold is 70,000 cells per milliliter.
Until those requirements are met and officials lift the advisory, treat it as active.
For students who just arrived in Boston, the useful habit is simple: check the latest public-health guidance before planning anything that involves getting into the Charles.
The river will probably become part of your Boston routine very quickly.
For now, enjoy it from land.
Advisory status and public-health guidance were checked on September 1, 2026 using current Boston Public Health Commission, Massachusetts Department of Public Health and Department of Conservation and Recreation guidance. Conditions and advisory boundaries can change, so check current official guidance before entering or having contact with the water.