Hundreds of trout have died at the Sparks Marina after the body of water turned over late last week. This die-off is not as severe as years past, but it's still leaving officials perplexed at its cause. 

"Basically, the warm water on top, and the cold water on the bottom, which has zero oxygen, actually mixed together, and for the third consecutive year, we have seen a trout die off at the Sparks Marina," said Chris Healy with the Nevada Department of Wildlife.

They know what killed the fish, but they don't know why this has happened the last three years, and not the years before.

NDOW, the University of Nevada, and the City of Sparks are looking into a solution. The investigation could last several months, if not more. 

Sparks Marina is also home to cat fish, carp, and bass. Those fish are fine because they don't need as much dissolved oxygen in their water. 

The City says they have tested the quality of water, and it is safe for humans and pets.  

"It is a natural aquifer, so the lake is constantly getting replenished daily," said Adam Mayberry with the City of Sparks. "It is safe for humans. It's safe for pets. Nothing changes." 

The marina is replenished by groundwater, which doesn't have oxygen. NDOW has restocked trout in the Sparks Marina several times this year, but put less because they feared another turnover. Regardless, upwards of 95% of the trout are caught within 45 days of being put in, according to NDOW. 

"We know through our data that fish that go into the Truckee River, or in this case, the Sparks Marina, they are caught within 30-45 days after being stalked," said Healy. "Yes, there are going to be some carry over fish, and in this case, we are seeing them go belly up in the marina."

The City of Sparks released this statement: 

Due to an unforeseen unique biological anomaly, the Sparks Marina is currently experiencing some die-off of fish.  This event is attributed to a “turnover” of the lake’s water due to the recent cold snap.
Lake turnover can occur when there is a drastic change in weather and the layers of water with noted temperature differences begin to mix together, and when water that has been sitting at the bottom of the lake begins to mix with the layers of water above it.  This can have an effect on a fishery such as the Sparks Marina.
The weather can cause dissolved oxygen levels to dip too low to sustain fish life, similar to what the Marina experienced in December 2013 and 2014 when there was a complete die-off of trout, catfish and bass caused from low oxygen levels in the water.
The City is working with Nevada Department of Wildlife (NDOW) officials and scientists at UNR to monitor oxygen levels to better understand the problem and possible remedies.  The impact of the low oxygen levels is dangerous to fish only. The water continues to be safe for dogs and people and there are NO public health or safety concerns at the Marina.
The water in the Sparks Marina is tested routinely.  The body of water is a 77-acre fresh water lake and is replenished daily from groundwater.  The City pumps on average 2.5 million gallons of water from the lake on a daily basis.