Fishing Union Reservoir CO Full Guide, Species, Spots, Tips

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Union Reservoir is a popular fishing destination located in Longmont Colorado. Situated against the backdrop of the stunning Rocky Mountains, this reservoir offers anglers a serene and inviting setting to indulge in their favorite pastime. The reservoir covers an area of approximately 736 acres and is renowned for its rich aquatic diversity and excellent fishing opportunities. Today we will guide through all the things that you guys need to know about fishing union reservoir.

The history of Union Reservoir dates back to its creation as an irrigation storage facility in the late 1890s. Over the years, it has evolved into a multifunctional recreational site that not only provides water storage but also offers a wide range of activities, with fishing being one of its most cherished attractions.

Anglers flock to Union Reservoir for a variety of reasons. The reservoir boasts a diverse fish population that includes species like rainbow trout, bass, catfish, and sunfish, providing a rich and varied fishing experience. Whether you’re an experienced angler or a beginner, the reservoir offers something for everyone. The calm waters and scenic surroundings create an atmosphere of tranquility that enhances the overall fishing experience.

One of the reasons why Union Reservoir stands out as a great fishing spot is its well-maintained facilities. Anglers can make use of fishing docks, piers, and shoreline access points, making it convenient to find the perfect spot to cast a line. Additionally, the reservoir offers opportunities for both boat and shore fishing, catering to different preferences and techniques.

The reservoir’s management actively promotes catch and release. And this is mostly contributing to the sustainability of its fish populations. This conservation minded approach ensures that future generations of anglers can continue to enjoy the thrill of fishing in these pristine waters.

Fishing Seasons Union Reservoir

The fishing experience at Union Reservoir in Colorado is greatly influenced by the weather and the changing seasons. Understanding how these factors interact with the reservoir’s aquatic ecosystem can significantly improve an angler’s chances of success. Here’s a detailed breakdown of how weather and seasonality impact fishing at Union Reservoir, along with some tips for each scenario:

Weather Conditions

  • Temperature: Temperature plays a crucial role in fish behavior. In colder months, such as winter and early spring, fish are more sluggish and tend to be deeper in the water to find warmer temperatures. As the weather warms up, fish become more active and move towards shallower areas.
  • Barometric Pressure: Rapid changes in barometric pressure, often associated with passing weather fronts, can affect fish activity. Fish are more likely to feed actively before a front arrives, and they might become less active during and after the front passes.
  • Wind: Wind can both positively and negatively impact fishing. A gentle breeze can create ripples on the water’s surface, making fish feel more secure and encouraging them to come closer to shore. However, strong winds can make casting difficult and disrupt fish behavior.


  • Spring: Spring is an excellent time for fishing at Union Reservoir as water temperatures start to rise. Fish become more active and move into shallower waters to spawn and feed. This is a prime time for catching bass and trout.
  • Summer: Summer offers the most consistent fishing conditions. Fish are often found in a wider range of depths, from shallow areas early in the morning and late in the evening to deeper waters during the day to avoid the heat. Targeting structures like underwater ledges, drop-offs, and submerged vegetation can yield good results.
  • Fall: Fall is another great fishing season as water temperatures begin to cool. Fish become more active again after the hot summer months. They start to feed voraciously in preparation for winter, making it an excellent time to catch larger, well-fed fish.
  • Winter: Winter fishing can be challenging due to cold water temperatures and fish being less active. However, some anglers still find success by using slow presentations and fishing in deeper areas where fish may gather to find warmer waters.

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Tips for Different Weather Conditions

  1. Pre-Frontal Conditions: Fishing before a weather front can be productive. Use a variety of lures and baits to capitalize on the increased feeding activity. Focus on areas with cover like rocks and submerged vegetation.
  2. Post-Frontal Conditions: After a front passes, fish might be more hesitant to feed. Use finesse techniques and smaller baits to entice bites. Fishing in deeper water where fish seek shelter from the changing conditions can also be effective.
  3. Early Morning and Late Evening: During hot summer months, fishing during the cooler parts of the day can be advantageous. Fish are more active, and you can target shallow areas with topwater lures and bait.
  4. Midday Summer Fishing: When the sun is high and temperatures peak, fish tend to move deeper to stay comfortable. Use deeper-diving lures or weighted bait to reach them.
  5. Fall Transition: As fall arrives, fish begin to migrate to shallower waters again. Look for areas with cover and structure near drop-offs as fish may be feeding in preparation for winter.
  6. Winter Tactics: Slow and subtle presentations are key during winter. Fish move sluggishly, so using techniques like jigging or fishing with live bait close to the bottom can yield results.

Adapting your fishing strategies based on the weather and seasonality can significantly enhance your success at Union Reservoir. Paying attention to the finer details of fish behavior and adjusting your approach accordingly will help you make the most of your time on the water.

Types of Fish in Union Reservoir

The fishing experience at Union Reservoir in Colorado offers a diverse and dynamic range of fish species, each contributing to an engaging and multifaceted angling adventure. From the variety of species available to the potential sizes they can attain, Union Reservoir provides an exceptional platform for anglers of all levels to enjoy a rich fishing experience.

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Diversity of Fish Species: Union Reservoir boasts an impressive variety of fish species, ensuring that anglers have a wide selection to target.

  1. Rainbow Trout: Renowned for their vibrant colors and energetic fights, rainbow trout are a prized catch at Union Reservoir. These fish are regularly stocked, maintaining a thriving population that entices anglers seeking a rewarding challenge.
  2. Largemouth Bass: Abundant and favored for their powerful strikes, largemouth bass offer exhilarating angling encounters. Their remarkable fighting ability and tactical behavior make them a prime target for those seeking excitement.
  3. Smallmouth Bass: While present in smaller numbers, smallmouth bass introduce an additional layer of diversity to the angling scene. These fish are known for their aggressive strikes and spirited battles, making them a favorite among many anglers.
  4. Catfish: The inclusion of various catfish species enriches the angling environment. Channel and bullhead catfish offer unique challenges and appeal to enthusiasts who relish a different type of angling experience.
  5. Bluegill and Sunfish: These panfish species provide accessible and enjoyable fishing opportunities, especially for beginners and families. Their consistent action and suitability for various angling techniques make them a perfect introduction to fishing.

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Fish Sizes and Growth Potential

The potential sizes that fish can attain in Union Reservoir add an element of anticipation and excitement to every fishing trip:

  • Rainbow Trout: Rainbow trout exhibit a wide size range, varying from a few inches to over 20 inches in length. Regular stocking ensures the possibility of encountering larger, more impressive specimens.
  • Largemouth Bass: Largemouth bass in Union Reservoir can span sizes from under a pound to well over 5 pounds. The reservoir’s fertile ecosystem offers the conditions for these bass to attain substantial sizes.
  • Smallmouth Bass: Smallmouth bass typically measure between 10 to 18 inches in length. This range presents the opportunity to engage with robust fish that are known for their spirited battles.
  • Catfish: Channel catfish and bullhead catfish encompass a range of sizes, from small individuals to those exceeding 20 inches. The growth potential of these catfish is influenced by the reservoir’s ecological factors, contributing to the diversity of catfishing experiences.
  • Bluegill and Sunfish: These smaller panfish species usually range from 4 to 8 inches in length. Although not the largest, they provide a steady and enjoyable angling experience, particularly for those new to fishing.

Final Thoughts

Union Reservoir in Colorado beckons anglers to a realm of diverse fishing encounters, where an assortment of fish species, spanning from rainbow trout to largemouth bass and catfish, populate its waters. From the anticipation of reeling in a robust smallmouth bass to the thrill of landing a sizable rainbow trout, the reservoir’s spectrum of fish sizes adds an extra layer of excitement, promising memorable and enriching fishing expeditions.

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