At Walden Ponds east of Boulder, receding water has left dead fish along the shoreline. Similar conditions are visible at Viele Lake and a pond along Wonderland Creek in the Kings Ridge neighborhood, where carp lie dead in stagnant, algae-filled water.
Across Boulder County’s plains, extreme drought is shrinking small lakes, ponds and wetlands. In some places, falling water levels have caused fish kills and foul odors. The damage can look permanent.
But city and county officials say many of these habitats are likely to recover when wetter conditions return. The immediate problem is that, even as the ponds dry, officials cannot simply refill them.
Many of the affected water bodies are artificial, including former mining pits that now depend largely on rain, runoff and groundwater. Some have no infrastructure through which water could be delivered. In other cases, the city or county lacks the legal right to divert scarce water into them.
Late-summer drying is not unusual. Hot weather increases evaporation, and shallow ponds and wetlands routinely lose water. This year, however, the effects have been magnified by prolonged heat and record-low snowpack, which have reduced runoff and groundwater recharge, according to the City of Boulder.
No water to send
Only about 20% of the wetlands managed by the city receive some water through irrigation, city spokesperson Jennifer Ciplet said. Many others have no delivery system connecting them to a water source.
“The city does not have a water source, a control mechanism, or a water right to fill these,” Ciplet said.
Colorado’s water rights system gives priority to those who began using water first. When a senior water user places a call, users with more junior rights may have to stop diverting water until the senior right is satisfied.
The current call on Boulder Creek extends to water rights dating to 1860, said Jeff Moline, Boulder County’s agricultural water specialist. That means rights established after 1860 are too junior to receive water under current conditions.
The City of Boulder holds some water rights dating to 1850 and is using them to maintain certain water bodies, including the Kids Fishing Pond in downtown Boulder, Ciplet said. The city is also using water to support flows in Boulder Creek.
Many smaller water bodies have far more junior water rights. They include a pond along Wonderland Creek in the Kings Ridge neighborhood. Walden Ponds, just east of Boulder, has water rights dating only to 2002.
“It’s way, way, way down in priority. We don’t have any water that we can send into Walden Ponds,” Moline said.
Although the county received some rain earlier in the summer, it was not enough to replenish the groundwater that feeds many of these water bodies, Moline said.
Conditions vary across the county. Pella Crossing, near Hygiene and west of Longmont, remains healthy because it receives fresh groundwater. Larger lakes and reservoirs are also generally being maintained.
City and county wetland regulations are intended to protect these environments from pollution, development and other human disturbances, not fluctuations in weather.
“It is not a violation of city code for a pond or wetland to experience lower water levels or be temporarily dry due to natural environmental conditions such as drought,” Ciplet said.
The strain extends beyond Boulder County. Colorado Parks and Wildlife has imposed dozens of drought-related restrictions and closures and is monitoring ecosystems where drought has complicated recovery after wildfires.
Denver Water closed Antero Reservoir to recreation for the season so its water could be redirected. Colorado Parks and Wildlife also authorized an emergency fish salvage at Westminster’s shrinking McKay Lake. Earlier this year, Boulder County farmers scaled back crops, staffing and community-supported agriculture programs because of the drought.
Ugly, but not necessarily permanent
Despite the visible stress, Mac Kobza, Boulder County’s wildlife management supervisor, said he has not seen evidence that the drought is causing irreversible damage to the lakes or their wildlife.
“In many ecosystems around the world, drought is a natural cycle,” said Kobza, who has worked in wildlife management for 26 years and specializes in aquatic ecosystems.
Many of the shrinking ponds are artificial and do not support the complex ecosystems found in natural lakes and wetlands. They are often populated by fish species such as largemouth bass, common carp and catfish.
Those ponds can struggle with low oxygen even during an ordinary summer. As temperatures rise and bacteria consume organic matter, oxygen levels fall, sometimes killing fish.
Removing dead or struggling fish is not necessarily better for the ecosystem, Kobza said, because it also removes nutrients that would otherwise feed insects, birds and other animals.
This year’s fish kills have provided food for invertebrates and birds, including bald eagles, Kobza said. Other birds can move to larger lakes where prey remains available. Drying ponds can also suppress invasive bullfrogs, which spread disease to native amphibians and are notoriously difficult to remove.
“Disturbance is part of an ecological process,” Kobza said. “These are the natural forces that regulate populations of wildlife and create opportunities.”
Native species are generally adapted to periods of drought and can retreat to remaining refuges until conditions improve, Kobza said. Unless creeks remain critically dry for an extended period, he expects most populations to recover.
“I haven’t, at this point, really had an indication that we’re seeing damage to the ecosystem where we’re losing native wildlife,” he said.
In many cases, Kobza said, the best option is to let nature run its course.
“There isn’t much we can do to stop it, especially in a high drought situation,” he said.
That can be difficult for residents confronted with dead fish, shrinking ponds and strong odors.
“I get the smell and the look is very bad. I understand that, but it is generally temporary,” Kobza said.
For now, the outlook for the affected ponds depends largely on the weather. More rain could begin replenishing groundwater, streams and floodplains. A stronger winter snowpack could improve runoff and water supplies next year.
“Hopefully we can start in a different spot next year,” Moline said.
