Zebra Mussels on Candlewood Lake: Facts vs Assumptions

Published January 2026

This article is a follow-up to my Instagram Reel: Instagram post. Zebra mussels are one of the most emotionally charged topics on Candlewood Lake, so this guide is intentionally written as facts vs assumptions, with primary sources linked throughout.

The short answer

Yes — zebra mussels have been documented on Candlewood Lake. The Candlewood Lake Authority (CLA) reports that in 2020, nearly 50 solitary zebra mussels were discovered on Candlewood’s shores and that the CLA has been assessing the state of the population. CLA – Conservation FAQ / Fast Facts

FirstLight (the owner/operator of the Rocky River pumped storage system) published that a report concluded zebra mussels were established throughout Candlewood Lake, capable of reproducing, and likely self-sustaining. FirstLight – Letter to Community Leaders (Aug 5, 2022)

Key definitions (why people disagree)

A lot of disagreement is really about definitions:

Detected / documented = confirmed observation(s) recorded.
Established = reproducing and sustaining a population.
Abundant = widespread and easy to find (this is not the same as “established”).

If two people are referencing different definitions (or different years), they can sound like they’re contradicting each other even when they’re not.

What official databases show (and what they don’t)

The USGS Nonindigenous Aquatic Species (NAS) database includes collection records for zebra mussels in Connecticut, including Candlewood Lake. USGS NAS – CT collection records (with disclaimer)

Important: USGS also states that collection records do not imply abundance and may not reflect the full distribution of established populations. That disclaimer is part of the reason “I’ve never seen one” can be true for an individual while records still exist for the lake.

You can also see the USGS distribution entry referencing Candlewood here: USGS NAS – zebra mussel distribution

Facts: how zebra mussels spread

Zebra mussels spread primarily through human movement of boats, trailers, and equipment—especially water trapped in bilges, livewells, ballast tanks, and other compartments.

This is why agencies emphasize “Clean, Drain, Dry” as the baseline prevention approach:

Connecticut also publishes best management practices for decontamination: CT DEEP – Best Management Practices for Vessel Decontamination (PDF)

Facts: what zebra mussels can impact

Zebra mussels are widely documented to attach to hard surfaces and create maintenance issues for boats and infrastructure. They can also alter aquatic ecosystems by filtering water. For general biology and impacts: USGS NAS – zebra mussel species profile

Common assumptions (and what the sources actually support)

Assumption 1: “If they’re in the lake, everyone will see them.”

Not necessarily. Visibility depends on where you are, what surfaces you interact with (dock ladders, rocks, intake grates, hulls), and timing. USGS explicitly notes that records don’t imply abundance. USGS NAS disclaimer

Assumption 2: “They’re only in one cove / one side of the lake.”

That’s difficult to confirm without current lake-wide survey results. CLA notes continued evaluation and provides zebra mussel resources and updates. CLA – Zebra Mussels

Separately, FirstLight’s 2022 letter references a report conclusion that zebra mussels were established throughout Candlewood and capable of reproducing. FirstLight – Letter (Aug 2022)

Assumption 3: “Winter drawdown solves zebra mussels.”

It’s more nuanced. Drawdown can expose shoreline surfaces to freezing conditions, which may affect organisms attached in exposed zones, but it does not equal complete elimination. Be cautious of anyone presenting drawdown as a guaranteed “solution” without specific study results for the lake.

Assumption 4: “If I haven’t seen them, they aren’t present.”

Individual experience is valid, but it isn’t a full monitoring program. That’s why agency guidance focuses on prevention behaviors rather than sightings alone: USFWS – Clean, Drain, Dry.

How to keep this topic calm and productive

If you’re trying to stay objective, the best approach is:

Anchor on primary sources (CLA, FirstLight, USGS, CT DEEP, USFWS)
Separate personal observations from lake-wide claims
Avoid assumptions about “everywhere” vs “nowhere” unless backed by monitoring data

License / representation note

I’m not a licensed real estate agent yet. This post is objective, informational, and based on publicly available materials about Candlewood Lake’s shoreline rules and management.

Zebra Mussels on Candlewood Lake