The city of Jacksonville sits near the mouth of the north-flowing St. Johns, where the river's 310-mile-long meander ends at the Atlantic Ocean. Bridges clogged with traffic span the tannic river and characterize modern-day man's passing relationship with Florida's mightiest and most historic waterway. Here's where the expedition starts, where our search for the source begins. This aerial view looks south, towards the headwaters.

Jacksonville, Florida is a river city in a state that boasts more than 11,000 miles of rivers, streams, and waterways. With a population of 736,000, Jacksonville is ever-expanding to accommodate its share of the state's steady stream of new residents and visitors -- 1,000 people every day. Riverfront restaurants like this attract visitors drawn by the opportunity to enjoy a riverside meal.

About a thousand people stream into the sunshine state every day, requiring more housing, more roads, more water. As the demands on the St. Johns are steadily increasing, many environmentalists are sounding the alarm about how much development the river can handle and still maintain its health and integrity. The groundwork for managing water resources was laid a quarter century ago; here, in northeast Florida, the St. Johns River Water Management District is responsible for striking the vital balance between conservation and use.

A team of documentary film producers and scientists sets out on houseboats, canoes, kayaks, airboats, and flying inflatable boats to take an up-close and personal look at the entire length of the St. Johns. Director and Executive Producer Wes Skiles attaches a high-definition camera to a kayak paddled by Producer Jill Heinerth of Karst Productions. Crew member Scott Braunsroth stands by with audio technician Joel Tower.

Director and Executive Producer Wes Skiles of Karst Productions has explored the far corners of the world and is now focusing his camera on a mighty waterway in his own backyard. A native of Jacksonville and resident of Florida, Wes grew up exploring the northernmost tip of this river but, in the course of this journey, will be seeing much of its 310-mile length for the first time.

Producer Jill Heinerth, a Florida resident, is one of the world's foremost cave diving explorers. Her technical skills and physical prowess will be put to the test during this journey when she dives into the subterranean world of springs that feed the St. Johns.

Houseboats are home base for the Karst film crew and scientists during this 10-day river journey from mouth to headwaters. The fact that this one is silhouetted by dark storm clouds is not an unusual sight. Five feet of rain per year falls on the St. Johns basin area.

The St. Johns River has a wide range of moods and personalities, often looking wildly Amazon-like, particularly after high-water events such as hurricanes.

Atlantic stingrays that live out their entire life cycles in fresh water are one of the unique inhabitants of the St. Johns River. We'll be meeting these creatures and a scientist who studies their intriguing relationship with this river later in the journey, on Lake Jesup.

Manatees find a hospitable habitat in the flat, grassy-bottomed St. Johns River. But they are affected adversely by increasing human encroachment on the river. And its not just motorboats they have to fear. The manatees that seek refuge in the warm waters of Blue Springs are dependent upon a healthy flow; a flow that could be impacted by increased development in the area.

In most places, the St. Johns River system is dark with tannins, but in some, it's crystal clear, such as here in the Silver Glen spring and tributary. Web documentary producer Kevin Sparkman dives among striped bass that hang out at the spring head.

The spring-fed Wekiva River, an important tributary of the St. Johns River, is a clear, tea-colored waterway. Local grassroots efforts serve to protect the all-important Wekiva watershed, a vital habitat for black bear, among other species.

Jim Maher, a scientist with the Florida Department of Environmental Protection in Jacksonville, signs the paperwork to deny a development permit because of its potentially adverse impact on the St. Johns River.

Jim Maher, with a crew from the Florida Department of Environmental Protection, hikes to a waterway in the greater Jacksonville metropolitan area to try to find the source of a problem pollutant. A sign on the fence warns people to stay away from the waterway due to a sewage leakage.

Jim Maher of the Florida Department of Environmental Protection in Jacksonville investigates a local waterway that recently and mysteriously developed a strange color and rank odor. The water eventually drains to the St. Johns.

Green algae and hairy white strings of bacteria blanket the bottom of this foul-smelling municipal creek. Like all waterways in these parts, its contents ultimately end up in the St. Johns.

Jim Maher of the Florida Department of Environmental Protection in Jacksonville addresses the fears of a concerned citizen who lives along a municipal creek that's plagued by a mysterious pollutant from a yet-unknown source. Maher explains the steps the DEP is taking to investigate and correct the problem.