There’s no viz like low viz

Interesting Research Related to Maritime Maine
By Charles H. Lagerbom | Apr 22, 2021
Photo by: Charles H. Lagerbom The author enjoys "awesome visibility" in the caves and grottoes at Kallithea Beach, Island of Rhodes, Greece.

As a scuba diver here in Maine, I often hear people ask how far you can see underwater. There is no real simple answer, it actually depends on a lot of different factors. First, we need to go over some definitions.

Visibility in diving is an estimation of the water’s clarity and is measured as distance in feet at which a diver can see horizontally. That visibility, however, can be greatly affected by light, topside weather, particles suspended in the water, and/or movement of the water itself. New England is rather notorious for not having all that great underwater visibility, especially when compared to warmer waters from more tropical or exotic climes.

“Divers call it “viz” as in “that was a great dive today, viz was good.” It is one of those things you always record in your dive log after the dive. More on dive logs later!

Visibility is also an important element that can make a dive exceptional or exceptionally difficult. I tend to think of it all as relative. Some days viz is good, other days not so much. Kind of like life itself.

The National Oceanic and Atmospheric Administration (or NOAA) Office of Marine and Aviation Operations defines low visibility for divers as “when visual contact with the dive buddy can no longer be maintained.” When this happens, you definitely make it a point to stick pretty close to each other in the murk.

The standard measurement for underwater visibility is the distance at which a Secchi disc can be seen. Created in 1865 by Angelo Secchi, an Italian priest and astronomer, the device is a simple white disc about 12 inches in diameter. Used to measure water transparency, it is usually mounted on a line and lowered into the water until no longer visible. The resulting measurement is the Secchi depth. The best visibility ever recorded was in Antarctic waters at 240 feet!

How far you can see underwater in Maine depends on many things. One factor is the composition of the water in which you are diving. Salinity gradients can mess up visibility, way more than its cousin, the better-known temperature thermocline. The saline gradient interface, or level where differing saline layers meet, is known as a halocline. Haloclines are usually found when diving near fresh water, like in estuaries or rivers.

If the halocline, or saline layers, get mixed or jumbled, as usually happens when you swim through them, the resultant loss of visibility can be incredible. Viz drops dramatically and everything just goes blurry. It even becomes difficult distinguishing shapes. I encountered one where I could not read my gauges, it was like I was looking through Vaseline or Jell-o. Others have referred to it as looking through boiling water, all bubbly and distorted. Rising above or descending below can quickly negate the effects.

Without doubt, a bigger factor is what is in the water. Turbidity is cloudiness or haziness caused by individual particles generally too small to be seen. Suspended particles such as sand, mud, clay, or other bottom sediments can dramatically reduce visibility, much like fog on land. Sometimes these darn particles can remain in suspension for quite a while, clay more so than sand or silt.

Currents, waves, run-off from storms, and other natural causes can also force these particles into suspension. We once did a check-out dive off Bayside a few days after a major storm had rolled through and visibility was less than 3 feet due to the churned-up waters and storm runoff. Not much fun!

The biggest cause of suspended particles reducing visibility, however, comes mostly from you or your dive buddy, like a fin or hand accidently brushing the bottom. All of a sudden, poof! Quickly losing visibility can actually cause major disorientation where you cannot even tell up from down. Scuba training teaches you in that case to try and watch your bubbles, since they will inevitably rise. So be careful not to stir up the bottom! This also teaches you to slow down while underwater. Low viz basically means being more methodical, measured in what you do.

Light no doubt helps with visibility, although it tends to have rapid attenuation through the water, especially as distance increases. That means there is a loss of flux intensity through the medium, in this case water. These effects vary with the light wavelength. This holds true for the sun’s position during different times of the year like autumn or spring. Cloudy or overcast days also affect visibility, as well as the sun’s position during the day, morning or afternoon dives and so on.

You would think having an electric light with you would help; some divers call them a torch. Yes, they do help, but not when things get stirred up. In fact, dive lights are pretty useless in high turbidity, low or zero viz conditions. They just reflect back the particles suspended — not helpful if you are searching for something. I have done quite a few search and recovery efforts by "feel" alone. More on that later!

Like suspended particles, organic particles can also kill good visibility. Maine waters are much clearer in winter and spring before algal blooms markedly decrease the distances you can see. Same is true in Maine lakes. Ice divers on the lakes in wintertime report excellent viz.

I once got called to find a mooring chain for a marina in Winterport. River diving is tough enough, with currents, haloclines, cold river water and all that, but this was like putting your head inside an inkwell. Absolute black! I literally could not see a thing, except the inside of my facemask. So, I pulled myself with one hand along a rope we had fixed to a dropped anchor out in the river, while I swept the immediate area with my other hand hoping to find and grab that mooring chain. We would reposition the anchor and I would go out again and again hoping it had fallen across the mooring chain.

We kept at it, since the slack tide time was limited and once the tide turned, the velocity of the river would quickly increase, and we’d be done for the day. Progress was pretty slow since it was all by touch alone, which can kind of creep you out if you let it. I would grab something and think…OK, that’s a rock…hmm, that’s a stick or a branch…uh-oh, that is something squishy (so let it go quick!).

When Front Street Shipyard in Belfast once lost some straps from its large boat lift, we dove in the lift bays with zero viz to find them. By feel alone, we recovered the several large strapping pieces that had been blown off the lift during a storm. Clouds and rain that day also did not help with the viz and mucking around the bottom sure stirred things up as well.

We retrieved golf balls from ponds at the Samoset Golf Course one time in zero viz because the bottom got so stirred up. Never saw a thing, but collected a few thousand balls, mostly by stepping or kneeling on them and somehow getting them into the net bag!

Another time on a search in zero viz, I put my hand through a large truck tire and practically screamed into my regulator until I realized it was not a giant eyeball or a mouth or something I had put my hand into! At times like that, in extremely limited or zero viz, it is all about your training and keeping a positive attitude.

In good conditions, visibility at most Midcoast Maine sites tend to be in the 15- to 20-foot range, sometimes more, oftentimes less. I consider it a good viz dive if I can see more than 5 feet. Photos or video off my GoPro are less than ideal when visibility is poor. This can be a consideration upon arrival at the dive site as to whether we even get into the water. Dives can be thumbed or not attempted if you do not feel comfortable with the conditions.

While attending my nephew’s wedding out at Lake Tahoe, I got the chance to dive the famous lake, renowned for its visibility. At high altitude, this huge mountain lake, formed by glaciers, is on the border between California and Nevada. My dive guide afterward apologized for the poor viz because that day apparently it was not their usual 100-plus-feet of visibility, but only 75 feet or so. For me, used to 10 feet or less, it was spectacular!

Visiting a sister on Whidbey Island, Washington state, I got a chance to dive in conditions very similar to Maine waters. Viz was pretty much like I was familiar with here in New England, lots of turbidity and low visibility. I felt totally at home and the experience was awesome!

On a dive during a family trip to Greece, visibility was some of the best I have ever encountered. The blue Aegean Sea seemed to go on forever. My dive off the island of Rhodes was at Kallithea, a vacation villa apparently used by Mussolini during World War II, when Italy occupied the country. Pretty surreal to enter this gorgeous patch of water from a nicely tiled waterfront veranda and explore the caves and grottoes where Il Duce vacationed. Water temperature was also pretty nice, and so was the ice-cold bottle of Alpha beer waiting for me afterward!

While seeing is important in diving, it is not everything. Sometimes you just do not have good visibility, while other times you do. Then there is diving at night, an entirely different yet also incredible scuba experience…more on that later!

Charles Lagerbom teaches AP U.S. History at Belfast Area High School and lives in Northport. He can be contacted at He is author of "Whaling in Maine," available through

Lagerbom dives the lift bays at Front Street Shipyard. (Photo by: Charles H. Lagerbom)
Lagerbom recovers strapping stacked on the float near mooring balls. Cloudy and rainy conditions were not helpful for visibility. (Photo by: Charles H. Lagerbom)
Visibility was about 10 to 12 feet at Keystone Ferry Landing at Fort Casey Underwater Park, Whidbey Island, Washington state. (Photo by: Charles H. Lagerbom)
Turbidity at the Keystone Ferry Landing dive was much like that encountered in Midcoast Maine waters. (Photo by: Charles H. Lagerbom)
The author found excellent visibility at about 40-foot depth, at Kallithea Beach, Island of Rhodes, Greece. (Photo by: Charles H. Lagerbom)
Pictured is Pietro Angelo Secchi (1818-1878), Italian astronomer and inventor of the Secchi disk to measure underwater visibility. (Photo in Public Domain)
If you appreciated reading this news story and want to support local journalism, consider subscribing today.
Call (207) 594-4401 or join online at
Donate directly to keeping quality journalism alive at
Comments (0)
If you wish to comment, please login.
Note: If you signed up using our new subscriber portal, your username is the email address you registered with and your password is in all caps