>> HOPEFULLY HE'S OKAY. >>> NOW TO A STORY A LOT OF PEOPLE IN BALTIMORE ARE TALKING ABOUT. THOUSANDS AND THOUSANDS OF DEAD FISH FLOATED TO THE SURFACE IN THE INNER HARBOR. A DISTURBING SITE WITH A STENCH TO MATCH. BUT WE ARE LEARNING WHAT HAPPENED. CRISTINA MENDEZ IS LIVE AT THE INNER HARBOR. YOU HAVE EVERYONE'S ATTENTION. AND WHAT HAVE YOU LEARNED? >> Reporter: EXPERTS ARE SAYING THESE FISH WERE OXYGEN STARVED AND THE FLUCTUATION BETWEEN THE WEATHER EARLIER THIS WEEK CAUSED A ROLE IN WHAT HAPPENED. >> OVER 1 MILLION FISH. I'VE BEEN WORKING AT THE AQUARIUM FOR 30 YEARS AND THIS IS THE WORST FISH KILL I'VE WITNESSED. >> Reporter: HE WORKS AT THE NATIONAL AQUARIUM AND SAID THE EXTREME HEAT DURING THE DAY AND COLD TEMPERATURE DIPS IN THE EVENING CAUSED A PHENOMENON CALLED THERMAL INVERSION. >> THE TOP LAYER OF THE BRACKISH WATER GETS DENSE AND IT GOES TO THE BOTTOM LIKE A CEILING FALLING DOWN. AND IT STIRS UP ALL THE INORGANIC MATERIAL. >> Reporter: THE BACTERIA TAKES OXYGEN OUT OF THE WATER AND THESE FISH DIED WHO HAVE A LOWER TOLERANCE FOR BAD WATER CONDITIONS. >> THIS IS A PRIMARY FOOD FOR THE OSPREYS AND IT'S REALLY A TRAGEDY. >> Reporter: IT WAS HARD TO MISS AND NOT JUST BY SITE. >> I WAS WALKING FROM FEDERAL HILL AND I COULD SMELL IT. >> Reporter: NOT ALL WAS LOST. THE NEW FLOATING EXHIBIT ACTED AS A REFUGE FOR SOME OF THE FISH THROUGH AERATORS. THAT COULD BE DONE TO EASE ENVIRONMENTAL PRESSURES. BUT I'M HAPPY TO SEE THE FISH IN THAT CHANNEL , INCLUDING SOME OF THESE THAT SWAM INTO IT AND LIVED TO THIS EVENT. >> Reporter: CITY WORKERS AND THE AQUARIUM STAFF DID THEIR BEST TO CLEANUP THE FISH OUT HERE, BUT ANY THAT REMAIN WILL DECOMPOSE AND