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San Juan River Midges
Midges in the pre adult stages are the most prolific food source for trout on the San Juan River.  They are present in large numbers from the upper to the lower river and are the most common food source available to trout on the San Juan most days of the year.  The 4 stage life cycle of Midges begins with fertilized eggs being deposited on the top of the water surface by females where the eggs sink to the bottom.  The eggs develop into small larva which are long, thin, segmented and tube shaped without noticeable external developed appendages.  Midge larva are generally found in the bottom structure of the river where they live in tube type cases burrowed into the river bottom or otherwise attach themselves to bottom material.  Midge larva are generally not considered mobile unless they are dislodged by current or motion, so Midge larva are not considered a major food source for trout.  Some Midge larva are thought to become mobile temporarily after current changes, especially decreases in flow.  Over time, the larva develop into Midge pupa which do become a significant food source for trout as the pupa rise to the surface and transform into adults.  Midge pupa have well segmented tapered bodies with a larger thorax that encases the developing head, wings and legs.  The body of the pupa form is "stockier" than the thin tube like bodies of the maturing larva and is more tapered as it is larger toward the front where the head, gills, wing cases and legs develop.  Pupa may also have small, featherlike gill structures extending forward from the head/thorax areas.  As with Midge larva, pupa are not considered to be very mobile except during the phase where pupa rise to the river surface to transform into Midge adults.  When Midge pupa are rising to the surface they have been shown to have mobility.  Moving a Midge pupa pattern toward the surface while fishing can sometimes induce a strike.  The emerging Midge pupa can be a very effective fishing pattern from the bottom of the river to the surface of the film where the pupa transforms into an adult by shedding its pupal shuck, drying its wings and flying away as an adult.  Midge pupa develop into small adults with 2 wings and 6 legs that leave the river once they escape the pupal shuck and dry their wings.  Females return briefly to drop their fertilized eggs in the rivers surface.  Single Midge adults on the San Juan are very small and difficult to fish as a dry fly unless done off a dropper using an indicator fly, however, some dry fly patterns that represent clusters of adult Midges/Midge emergers can be very effective on the surface.  San Juan Midge's come in several colors and sizes including cream, olive, red, black and a white and black zebra pattern.  Most Midge patterns on the San Juan are size 20-28.  Once the Midge pupa transform into adults and leave the surface of the river they are no longer available to trout as a major food source.  During a day's fishing on the upper river it is common to come across hundreds of newly discarded pupal shucks floating on top of the water or pushed toward shore by the winds.  In the colder sections of the river near the dam Midges and annelids are the primary food sources for trout as Mayflies, caddis and stoneflies do not show up in large numbers until the water warms downstream.  In addition to being the dominant food source near the dam, strong Midge populations continue downstream through all of the Quality Water and below.  If you can become a skilled Midge fisherman and accurately match the Midge hatch of the day you can have success on the San Juan almost any day of the year.  

Modern Midges by Rick Takahashi & Jerry Hubka

San Juan River Mayflies
 Mayflies represent the food source most commonly associated with fly fishing.  Historically speaking, the early English fly fishers considered fishing dry flies on the surface to imitate hatching Mayflies the most elevated form of fly fishing.  As fly fishing has evolved over the years it has become apparent that in addition to trout feeding on newly emerged mayfly duns on the rivers surface, they also feed on Nymphal mayfly forms, mayfly emergers and mayfly spinners which have reached the end of their life cycles.  Stomach samples indicate that the various Nymphal forms and mayfly emergers are the most common of the mayfly food sources.  As with Midges, Mayflies begin with the female depositing fertilized eggs at or below the waters surface.  These eggs sink to the bottom and develop into Nymphs forming a distinct head, small antennae, thorax with wingpads, legs, a segmented and tapered abdomen with gills down the sides and 2 - 3 short tails.   Mayfly Nymphs have an external skeleton which may be discarded several times as the size of the Nymph increases.  After molting, the mayfly Nymph develops a new external skeleton from its outer skin surfaces.  Various mayfly species prefer different bottom and current speeds making the Nymphal form available to trout in many different water types.  Most mayfly species are considered to have a year long lifespan from egg to adult, so there is an extended development time as the Nymph develops into an adult.  Mayfly Nymphs are mobile with the ability to move through the bottom and current becoming noticeable to trout as a food source at these times.  Once the Nymphs develop fully they rise to the surface of the water, shed their Nymphal exoskeleton and emerge as an air breathing, sexually immature mayfly dun.  The mayfly dun is present on the water surface only long enough to fully shed the Nymphal exoskeleton and dry the wings, but this takes a few monents.  During this period the Mayflies may appear on the surface of the water with their wings upright in a "sailboat" type shape.  Once the wings dry, the duns quickly escape to nearby streamside vegetation where they continue maturing into adults.  Within a day or two, the duns finish maturing into sexually mature imago's, mate, deliver fertilized eggs to the water and then die as spinners.  The San Juan has mayfly hatches virtually every month of the year of the small "baetis" variety, commonly called Blue Winged Olive.   In addition, a larger Pale Morning Dun comes off in  mid to late summer months. 

Modern Midges by Rick Takahashi & Jerry Hubka

Annelids and Aquatic Worms
The San Juan worm pattern is well known throughout the fly fishing community as an effective Nymph pattern.  The reason for this in the San Juan River is that there are several Aquatic Worm species available to trout, generally year round.  These species are present in the Quality Water as well as the Lower River.  Usually these are small worms, generally less than 2" that are available in different colors including tans and reds.  Often, small midges in the larval form resemble "worms" and are mistakenly identified by fishermen as annelids. 

The San Juan River provides Caddis as a food source for trout in the lower portions of the Quality Water.  As with Mayflies and Stoneflies, Caddis do not reproduce well in a the constantly cold temperatures near the dam.  The warming and more seasonal waters downstream do support Caddis populations, especially in the lower stretches of the Quality Water and Lower River.  The life cycle of Caddis is similar to Mayflies and Midges in that there are 4 life stages including the egg, larva, pupa and adult.  Fertilized eggs are deposited on the water surface or on the stream bottom by "diving" caddis females.  The eggs develop into Caddis larva which develop over time into pupa.  There are many different types of Caddis larva and they utilize some unique strategies to protect the developing larva.  Some caddis larva are feee living and are exposed to trout as they move about the bottom of the stream.  Other caddis larva build protective shelters such as nets or pebble/debris cases, still others burrow into the sand similarly to Midge larva.  Caddis larva have a distinctive head and thorax from which 6 legs project, usually claw shaped on the ends.  The abdomen is segmented with 2 small hooks on the bottom of the abdomen and long in comparison to the head and thorax area.  Caddis larva do not have pronounced antenna or tails.  The San Juan contains both cased and non cased (free living) caddis species.  As caddis larva continue to grow they mature into a pupa which develops wings, air breathing apparatus and the sexual organs necessary for reporduction.  At the end of this pupation period which may require several weeks, the fully developed pupa rises to the surface, discards its pupal case, quickly dries its wings and flies away.  In contrast to the emerging mayfly, this process is generally swift requiring fish who are feeding on emerging caddis pupa/adults to move quickly.  If you are seeing fish feed on the surface in quick strikes they are likely taking the quickly moving caddis pupa or adults. 

Golden Stoneflies
There are small quantities of Golden Stoneflies present in the Lower Quality Water and Lower River.  These insects are relatively large in comparison to the Midges and Mayflies normally fished on the river. 

As with other western trout rivers, terrestrials are a food source for trout on the San Juan when they are available.  During the summer and early fall traditional terrestrials such as beetles, ants and grasshoppers become available to trout.  In some years the first hard summer rain moves large numbers of ants into the river providing exceptional top water fishing using ant imitations.  Grasshoppers can be found during summer months along grassy banks and are an opportunistic food source for trout.  The intermittent presence of terrestrials on the river provides the opportunity to fish larger attractor patterns on the surface. 

Forage Fish
The San Juan offers smaller forage fish in most parts of the river.  Some of these are the young from naturally spawning Rainbows and Browns.  Browns have not been stocked in the river since 1997 so natural reproduction has been the exclusive source of Browns since that time.  Rainbows are also considered to spawn in the river, however, it is difficult to assess how successful Rainbow spawning is.  Estimates are that only about 5% of Rainbows spawn.  There are also some smaller fish from spawning carp in the slack waters near the river.  It is very unusual to catch carp in the main parts of the river.  The state stocks Rainbows in the 4-5 inch range in the STW (Quality Water) - these smaller trout can be targets of the larger trout in the area.  Larger trout are stocked downstream of the Quality Water.  The Lower River contains sculpins and the young of other native species.