Aquatic Plants and Algae ID

A directory of known plants and their characteristics that have been seen in Harbor Isle Lake -- many of which are invasive and should be appropriately removed and managed.

Cattail (invasive aquatic plant)

[Southwest Florida Water Management District - Not Recommended Aquatic Plant - High Maintenance]

Though most cat-tail or typha species in Florida are native, they often grow to cover large areas of lakes quickly and aggressively through their extensive rhizome root structure, overpowering other more beneficial slower growing aquatic plants. They must be controlled consistently or more shoreline is lost year over year.

Their dying, brown leaves fall into the lake and decompose-- releasing Nitrogen and Phosphorous into the lake, adding to the organic sediment and nutrient load.

Their 10+ feet height block the view/access of the water, especially critical when trying to observe toxic blue-green algae blooms. They also prevent wildlife from fishing at the shore and having other food sources.

They capture the floating scum mats of toxic blue-green algae due to their stagnant water. The stalks then hold the drying toxic scum residue-- increasing airborne exposure of toxins via the residue's dust.

Invasive Plant-- If a systemic herbicide is not used to kill to the root, removal must be made from the root or rhizome directly, by physical removal. Otherwise, they will grow back and fill in.

The City used to manage the control of cattails, under Storm-water Management, yet since 2019 they have ignored resident's requests for spraying. The City has not engaged in any mechanical removal for lake access, despite having the permit and resources to do so.

Duckweed (invasive floating plant)

Hydrilla (invasive & non-native submerged aquatic plant)

[Federal Noxious Weed List ]

Characteristics: Stems are slender, branched and up to 25 feet long. Hydrilla’s small leaves are strap-like and pointed. They grow in whorls of four to eight around the stem. The leaf margins are distinctly saw-toothed. Hydrilla often has one or more sharp teeth along the length of the leaf mid-rib, produces tiny white flowers on long stalks. It also produces 1/4 inch turions at the leaf axils and potato-like tubers attached to the roots in the mud.

Can grow in only a few inches of water, or in water more than 20 feet deep, Reproduces mainly by regrowth of stem fragments; also reproduces by growth of axillary buds(turions) and subterranean tubers; tubers can remain viable for more than 4 years

Invasive and Non-native Plant -- Hydrilla is an invisible menace, invisible that is until it fills the lake or river that it infests, “topping out” at the surface. Hydrilla can grow an inch a day. Control is difficult, the best practice is to try and remove what can be seen, roots included. Herbicides provide temporary control.

Filamentous Algae (many species types)

Characteristics: Single algae cells that form long visible chains, threads, or filaments, these intertwine forming a mat that resembles wet wool

Filamentous algae starts growing along the bottom in shallow water or attached to structures in the water (like rocks or other aquatic plants). Often, filamentous algae floats to the surface forming large mats, which are commonly referred to as “Pond scums.” There are many species of filamentous algae and often more than one species will be present at the same time in the pond.

Characteristics: Can be toxic, Green paint or guacamole-like water, scum mats form when bacteria blooms, these can increase when winds push the bacteria into one area, when this builds up, it can start to smell and it is a noxious and foul odor.

Contact, ingestion and inhalation should be avoided to reduce risk of health effects. Exposure to cyanobacteria is currently being studied and possibly linked to higher risks of neurodegenerative diseases such as ALS, Alzheimer's, and Parkinson's.

Harbor Isle Lake predominantly has microcystis aeruginosa, which releases the microcystin toxin.

Alligatorweed (invasive & non-native aquatic plant)

[Florida Prohibited Aquatic Plants List]

Characteristics: Alligator weed can grow in a variety of habitats, although it is usually found in water. Sometimes it forms sprawling mats along shorelines. Alligator weed is an herb that occurs throughout Florida and flowers in the warm months. It has smooth stems that trail along the ground or out across the water. The stems are hollow. They have nodes from which other stems and roots grow.

Invasive and Non-Native Plant-- physical removal for control

Chara (green algae type)

Algae ID Comparison

If you observe characteristics, like those shown for blue-green algae, please exercise caution in and around the water.

It is encouraged to report observations of a bloom to the DEP, at the link below:

https://floridadep.gov/dear/algal-bloom/content/algal-bloom-sampling-results

Image Chart Courtesy of: https://www.minnehahacreek.org/explore/blue-green-algae-faq