Other marine life
Troll Hair Algae
Filamentous freshwater algae (unidentified; locally 'trollahár')
The bright green filamentous algae that grows along Silfra's lava rock and is the most visible living thing in the fissure. Icelandic operators call it trollahár — troll hair. It is the reason the Lagoon reads green rather than grey, and it is the closest Silfra comes to a biology draw.
- Max size
- Filaments to roughly 1m, trailing over rock
- Habitat
- Lava rock and boulders through the fissure, strongest in the shallow, well-lit Silfra Lagoon
Best places to dive with Troll Hair Algae
| Month | Likelihood |
|---|---|
| January | commonly seen |
| February | commonly seen |
| March | commonly seen |
| April | commonly seen |
| May | commonly seen |
| June | commonly seen |
| July | commonly seen |
| August | commonly seen |
| September | commonly seen |
| October | commonly seen |
| November | commonly seen |
| December | commonly seen |
Present year-round throughout the fissure; no seasonal peak. Most obvious in the shallow Lagoon where light reaches.
Sources & last checked
Checked July 2026
This is a researched draft, not yet human-verified. The seasonality and logistics are drawn from the sources below — confirm specifics (permits, fees, closures) with an operator before you book.
- Dive Site Silfra — DIVE.IS
- Iceland Silfra Fissure — Diving & Snorkeling — Arctic Adventures
Note on the data: Named colloquially by operators rather than identified to species in any source found; recorded here as a local common name for filamentous algae.