Leaf Rakes are deep nets made for swimming pool maintenance and available from any pool supply store. Cost is $12 to $40 with average around $20. They're attached to a standard pool extension pole, about $20. They can be dragged along the pond's bottom to get muck. However in heavy muck the net can get very heavy because water is slow to drain through the muck and out the net so you can end up lifting 30-50 pounds of water on the end of the pole. We've bent metal poles in half doing this.
Because of the effort involved using a Leaf Rake they become less helpful the larger the pond especially when there's a thick layer of muck. They're useful in larger ponds for getting leaves floating on the pond surface before they can stink to the bottom. Also useful for getting some leaves off the bottom when muck isn't too thick. There main advantage is fast setup and storage, pretty much just pick up and use.
Some fish and other critters will end up in the net when dragged along the bottom so ponders with small fish need to check the bag when dumping. Also dump it near where you're working and keep an ear open for the sound of flopping around.