It’s hard not to get blown away by the clarity of Lake Tahoe’s waters. Peering into the depths, you can spot twigs, rocks, and (sadly) trash 20 or even 30 feet down. You’d swear you were sitting on top of a giant aquarium. Biologists measure this transparency with a device called a Secchi disk, which is really nothing more than a white circle. The disk is lowered into the water until it disappears from view, with that depth being recorded as the Secchi depth. Tahoe typically produces Secchi depths of 67 feet. Under these incredibly clear conditions, fish can see your fly from many yards away.
The situation is often quite different in the state’s lowland ponds, lakes, and reservoirs. With higher nutrient levels and warmer temperatures, these still waters are more fertile and frequently develop algal blooms. Unlike regular pondweeds, blooms are composed of microscopic single-celled plants suspended in the water column. Secchi depths during such blooms may range from a few feet to a few inches. Not surprisingly, fish won’t be able to see your fly from a great distance during a bloom. Standard flies and techniques still catch fish, but there’s no denying that the reduced visibility can make things more challenging. To succeed in these situations, you’re going to have to help the fish find your fly.
Tea or Soup?
As you walk along the shore, wade out, or launch your watercraft, take the time to look down and gauge the water’s transparency. Depending on a number of factors, an algal bloom may create nothing more than a slight discoloration of the water or something that more closely resembles a veggie smoothie. It’s also a good idea to recheck the transparency regularly, since the density of blooms can change, depending on factors such as location, time of day, and wind. You may start the day fishing in a light green tea, only to find that a couple of hours later, your flies are sitting in a pea soup.
As with so many things in fly fishing, a basic understanding of biology can be very helpful. This is certainly true with algal blooms. Thankfully, most of what you need to know can be condensed into a few short paragraphs. Don’t worry, you won’t need a microscope or the ability to pronounce “Aphanizomenom.”
Nutrients
Just like plants on land, algal blooms require nutrients. Runoff from winter storms usually delivers fresh nutrients to ponds and lakes, while waves stir up the shallows, releasing nutrients stored in the sediments. As long as the supply of nutrients exceeds the demand, the algae will keep blooming. Eventually, however, the sheer number of algae in the water will use up one or more of the nutrients, causing the bloom to die off. Sometimes this happens gradually, and you’ll notice that the water becomes a bit clearer each day. But there are times when the bloom “crashes,” and within the space of 24 to 48 hours, the water goes from murky to clear. Whether it’s a gradual die-off or a crash, this process releases nutrients back into the water, and another bloom usually starts in a few days. This cycle of blooming and clearing can repeat throughout the summer and fall.
Diatoms
These tiny, single-celled algae produce the type of bloom you’re most likely to encounter in the early spring and late fall. They are able to thrive when day lengths are short and the water tends to be cool, but not cold. They can do this because they have photosynthetic pigments that allow them to capture sunlight more effectively than regular green algae. You’ll know when you are seeing a diatom bloom because these extra pigments absorb quite a bit of green light. This gives diatom blooms a tan, brown, or reddish color. Though they are less common, dinoflagellate blooms (unrelated to diatoms) produce similar water coloration to diatoms. Diatoms are food for zooplankton (small planktonic animals such as daphnia), and it’s not unusual to find both in large numbers. My underwater tests suggest the most visible fly colors in diatom blooms are silver, pink, white, and black. Brown and red tend to be the first to disappear.
Green Algae
Most of the year, green algae will be the reason why the water in a pond or lake isn’t crystal clear. As their name suggests, these tiny plants have photosynthetic pigments that ref lect, rather than absorb green light. This puts them at a slight disadvantage to diatoms in the spring, but the longer days and stronger sunlight of summer and early fall give them the upper hand. Like diatoms, green algae blooms can also support a lot of zooplankton. I have found the most visible colors during green algae blooms are silver, pink, red, and white. Greens and chartreuse quickly disappear into the background.
Blue-Green Algae
The scientific name for blue-green algae is cyanobacteria. They contain photosynthetic pigments, like algae, but as their name suggests, are actually a form of bacteria. Blue-greens are found in all lakes, but tend to dominate in those with higher nutrient levels and warmer waters. They can bloom in the spring, but tend to be more pronounced in the late summer and fall. In general, my tests have shown the best fly colors for blue-green blooms are similar to those for green algae. That said, blue-green blooms are often more vibrantly green than green algae blooms, which tends to make chartreuse even less visible.
In waters with very high nutrient levels, the blooms can become very soupy, especially if wind drives the cyanobacteria into shallow bays or inlets. Water transparency under these conditions is measured in millimeters or less. The downwind edge of the lake will often develop a blue-colored scum. Not surprisingly, with millimeters of visibility, fishing with anything other than stinky baits is close to impossible.
Actually, concerns about visibility aren’t as significant as concerns about health. Blue-green blooms can produce two types of toxin. One targets the liver, while the other hits the nervous system. Both have the ability to sicken and kill animals. I have seen a couple of really bad blooms that resulted in the death of hundreds of coots and herons. Humans are not immune, as I found out while conducting toxin tests at a nearby lake many years ago. I got a really bad headache and full-body muscle aches that lasted for 32 hours. A week later, a grad student developed numbness and stinging-nettle sensations in both hands. Both cases were consistent with exposure to a neurotoxin produced by the bloom.
What triggers blue-greens to produce toxins is unclear, but it can happen rapidly. Tests taken as little as 12 hours apart can go from undetected to levels way above the state health limit. While health authorities are becoming more aware of this problem, toxin testing at most lakes is infrequent, and small ponds are likely never tested. If you arrive at a lake or pond with an active bloom and notice it is posted with warning signs, it’s probably best to find another place to fish. You may be fine, but there’s just no way of knowing for sure.
Optical Boosters
OK, having dealt with the biology, it’s time to address how to fish in blooms. First, it’s important to understand the difference between looking down into water and looking through it. Believe it or not, you see quite a bit farther when looking straight down into the water. For example, three feet of vertical visibility may translate to only one foot of lateral visibility. While fish have better vision than submerged humans, the laws of physics still apply. The more discolored the water, the more your fly needs to stand out.
If water clarity isn’t too bad, standard fly patterns and fishing techniques are often fine. Accurate casts that place the fly close to rising trout or pieces of bassy structure will still produce. That said, even with a light bloom, it can often pay to give the fly a bit of an optical boost. For example, choosing a shiny Chromie-style chironomid pupa or a nymph with a fluorescent hot spot can help make it stand out. If you are fishing for bass, try patterns that incorporate Flashabou or fluorescent materials.
If the bloom is on the soupy side, visibility may be measured in inches. This is going to make it much harder to score with smaller flies, especially ones that are similar to the color of the surrounding bloom. A trout will almost have to bump into an olive-colored nymph when the surroundings are green. You can switch to patterns that feature shiny, fluorescent, or glow-in-the-dark materials, but don’t expect to draw fish from great distances. Fortunately, there are a couple of tricks that can help in these conditions.
If you are after trout, forget about using typical insect patterns and try a flashy streamer instead, something that matches the size of fry or baitfish in the lake, but with a healthy helping of Flashabou. Even if there is an insect hatch going on, trout will often take a streamer. A tail or throat tag of fluorescent material can also help, but use something that’s not the same basic color as the bloom.
Trout Slappers
If you don’t want to work a streamer, try a large floating pattern such as a bee imitation or Booby and hang a nymph from a dropper a foot or so below. The impact of the fly on the water can help the fish locate it, since the sensitivity of their hearing and lateral lines isn’t affected by the bloom. In the case of hatchery-reared fish, slapping the fly on the water can create a sound similar to what’s made by a food pellet. You can even tie or buy a fly called the Pellet, which is a match-the-hatch pattern for trout chow. This may not be an “upstream dry fly, old chap” approach, but on really tough days, you might want to try one. You can also use the slapped-fly delivery technique with holdover fish that have been in the water for a year or more. Whether they assume it’s a pellet or a fat, juicy terrestrial insect I can’t say.
Bass Boosters
Largemouth bass have no trouble getting big and fat in waters with clarity that’s often measured in inches. Even if the fish can’t see their quarry, they’ll often pick up any sounds or vibrations the prey might make. Many f ly fishers consider bass fishing a top-water game. There’s no denying this is the most exciting way to catch them. Drop a frog pattern next to a dock or downed tree, give it the occasional twitch, and wait for the explosion. Even in soupy waters, bass will hear or feel the fly and home in on it.
But frogs aren’t the only thing that ends up inside largemouth bass. Dragonflies, mice, snakes, and birds will often end their lives as bass food. A conventional-tackle bass-angling friend showed me a picture of a five-pound bass he had caught the day before. At first, I couldn’t see why he was so excited. Bass of this size aren’t exactly uncommon in the lake. Then he said, “Look inside the mouth,” and I noticed the legs and tail feathers of a jay-sized bird. With a grin that threatened to split his face in half, he explained how he had caught the fish on a large top-water lure dropped next to some downed tules. Apparently, this was a spot where he noticed birds regularly take a drink, and he figured it might attract a big bass.
Not surprisingly, bigger flies make more of a disturbance, and this can be helpful in a bloom. If you are comfortable chucking big flies, try throwing an extralarge frog or rodent pattern. But be careful not to overdo things. On heavily pressured waters, bass know how the real McCoy sounds, and an extrahard pop will often send them deep into cover. Start softly and let the bass tell you how animated they want their food to be. If you aren’t comfortable throwing rodent-sized flies, try a dragonfly pattern. These often work much better with the slap delivery, followed by a few tiny twitches.
Subsurface Noises
When the water gets murky, conventional bass anglers often select lures that create sound and vibration. Fly fishers can do this by using patterns that incorporate small rattles. If your favorite bass flies don’t have rattles, try the cheap, slipon rattles that conventional-tackle anglers use. They work very well with flies mounted on jig and worm-style hooks.
If you find yourself fishing in a particularly thick bloom, try using flies that produce a lot of flash and vibration. Patterns that feature a small spinner, such as the Spinster, or a wobbling blade like the Coyote can work wonders under these conditions. You can even add wobbling blades to regular patterns tied on larger jig or bass worm hooks. For instance, the blade from a small Mepps or Panther Martin spinner can be attached to the snap on a small snap swivel. Simply slip the eye of the swivel onto the shank of the hook and hold it in place with a quarter-inch section of 1-millimeter silicone tubing. This will morph your fly into a small version of the conventional bass angler’s underspin lure. The amount of flash and vibration from this setup will be orders of magnitude more than you can produce with any conventional fly. This may not follow the Marquis of Queensbury rules of fly fishing, but it’s better than getting skunked.
As we head into a drought year, algal blooms are going to be a reality on many of the state’s still waters. While this may not be ideal for “normal” fly fishing, it’s far from an exercise in futility. Fish still need to feed during algal blooms, and that means they can be caught. You just have to think and fish a little differently.
